<?xml version="1.0" encoding="US-ASCII"?>  
<!-- Generated by CompSci Transform (tm) - http://www.compsciresources.com -->    
<!-- Created: Tue Feb 10 02:04:22 UTC 2026 -->  
<xs:schema elementFormDefault="qualified" xmlns:bacq="http://www.BleichroederAcquisitionCorp.I.com/20250930" xmlns:srt-types="http://fasb.org/srt-types/2025" targetNamespace="http://www.BleichroederAcquisitionCorp.I.com/20250930" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:us-types="http://fasb.org/us-types/2025" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:dtr="http://www.xbrl.org/dtr/type/2024-01-31" xmlns:xbrli="http://www.xbrl.org/2003/instance">     
  <xs:annotation>   
    <xs:appinfo>  
      <link:linkbaseRef xlink:type="simple" xlink:href="bacq-20250930_lab.xml" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef"/> 
      <link:linkbaseRef xlink:type="simple" xlink:href="bacq-20250930_pre.xml" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef"/>   
      <link:linkbaseRef xlink:type="simple" xlink:href="bacq-20250930_def.xml" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef"/> 
      <link:linkbaseRef xlink:type="simple" xlink:href="bacq-20250930_cal.xml" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef"/>  
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ConsolidatedBalanceSheet" id="bacq_r_ConsolidatedBalanceSheet">    
        <link:definition>001 - Statement - Condensed Consolidated Balance Sheets</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ConsolidatedBalanceSheet_Parentheticals" id="bacq_r_ConsolidatedBalanceSheet_Parentheticals">    
        <link:definition>002 - Statement - Condensed Consolidated Balance Sheets (Parentheticals)</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ConsolidatedIncomeStatement" id="bacq_r_ConsolidatedIncomeStatement">     
        <link:definition>003 - Statement - Condensed Consolidated Statements of Operations (Unaudited)</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ShareholdersEquityType2or3" id="bacq_r_ShareholdersEquityType2or3">   
        <link:definition>004 - Statement - Condensed Consolidated Statements of Changes in Shareholders&#8217; Deficit (Unaudited)</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ConsolidatedCashFlow" id="bacq_r_ConsolidatedCashFlow"> 
        <link:definition>005 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/DescriptionofOrganizationandBusinessOperations" id="bacq_r_DescriptionofOrganizationandBusinessOperations">   
        <link:definition>006 - Disclosure - Description of Organization and Business Operations</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SignificantAccountingPolicies" id="bacq_r_SignificantAccountingPolicies">    
        <link:definition>007 - Disclosure - Significant Accounting Policies</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/InitialPublicOffering" id="bacq_r_InitialPublicOffering">   
        <link:definition>008 - Disclosure - Initial Public Offering</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/PrivatePlacement" id="bacq_r_PrivatePlacement">   
        <link:definition>009 - Disclosure - Private Placement</link:definition>     
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/RelatedPartyTransactions" id="bacq_r_RelatedPartyTransactions">    
        <link:definition>010 - Disclosure - Related Party Transactions</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/CommitmentsandContingencies" id="bacq_r_CommitmentsandContingencies">     
        <link:definition>011 - Disclosure - Commitments and Contingencies</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ShareholdersDeficit" id="bacq_r_ShareholdersDeficit">    
        <link:definition>012 - Disclosure - Shareholders&#8217; Deficit</link:definition>     
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/FairValueMeasurements" id="bacq_r_FairValueMeasurements">   
        <link:definition>013 - Disclosure - Fair Value Measurements</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SegmentReporting" id="bacq_r_SegmentReporting">   
        <link:definition>014 - Disclosure - Segment Reporting</link:definition>     
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SubsequentEvents" id="bacq_r_SubsequentEvents">   
        <link:definition>015 - Disclosure - Subsequent Events</link:definition>     
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/AccountingPoliciesByPolicy" id="bacq_r_AccountingPoliciesByPolicy">   
        <link:definition>996000 - Disclosure - Accounting Policies, by Policy (Policies)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SignificantAccountingPoliciesTables" id="bacq_r_SignificantAccountingPoliciesTables"> 
        <link:definition>996001 - Disclosure - Significant Accounting Policies (Tables)</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/FairValueMeasurementsTables" id="bacq_r_FairValueMeasurementsTables">     
        <link:definition>996002 - Disclosure - Fair Value Measurements (Tables)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SegmentReportingTables" id="bacq_r_SegmentReportingTables">     
        <link:definition>996003 - Disclosure - Segment Reporting (Tables)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/DescriptionofOrganizationandBusinessOperationsDetails" id="bacq_r_DescriptionofOrganizationandBusinessOperationsDetails">  
        <link:definition>996004 - Disclosure - Description of Organization and Business Operations (Details)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SignificantAccountingPoliciesDetails" id="bacq_r_SignificantAccountingPoliciesDetails">   
        <link:definition>996005 - Disclosure - Significant Accounting Policies (Details)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofValuationofThePublicRightsTable" id="bacq_r_ScheduleofValuationofThePublicRightsTable">   
        <link:definition>996006 - Disclosure - Significant Accounting Policies - Schedule of Valuation of The Public Rights (Details)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofClassAOrdinaryShareSubjectToPossibleRedemptionTable" id="bacq_r_ScheduleofClassAOrdinaryShareSubjectToPossibleRedemptionTable">   
        <link:definition>996007 - Disclosure - Significant Accounting Policies - Schedule of Class A Ordinary Share Subject To Possible Redemption (Details)</link:definition>     
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofBasicandDilutedNetIncomePerOrdinaryShareTable" id="bacq_r_ScheduleofBasicandDilutedNetIncomePerOrdinaryShareTable"> 
        <link:definition>996008 - Disclosure - Significant Accounting Policies - Schedule of Basic and Diluted Net Income Per Ordinary Share (Details)</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/InitialPublicOfferingDetails" id="bacq_r_InitialPublicOfferingDetails">  
        <link:definition>996009 - Disclosure - Initial Public Offering (Details)</link:definition>    
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/PrivatePlacementDetails" id="bacq_r_PrivatePlacementDetails">  
        <link:definition>996010 - Disclosure - Private Placement (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/RelatedPartyTransactionsDetails" id="bacq_r_RelatedPartyTransactionsDetails">   
        <link:definition>996011 - Disclosure - Related Party Transactions (Details)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/CommitmentsandContingenciesDetails" id="bacq_r_CommitmentsandContingenciesDetails">    
        <link:definition>996012 - Disclosure - Commitments and Contingencies (Details)</link:definition>     
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ShareholdersDeficitDetails" id="bacq_r_ShareholdersDeficitDetails">   
        <link:definition>996013 - Disclosure - Shareholders&#8217; Deficit (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofCompanysAssetsandLiabilitiesTable" id="bacq_r_ScheduleofCompanysAssetsandLiabilitiesTable">  
        <link:definition>996014 - Disclosure - Fair Value Measurements - Schedule of Company&#8217;s Assets and Liabilities (Details)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/SegmentReportingDetails" id="bacq_r_SegmentReportingDetails">  
        <link:definition>996015 - Disclosure - Segment Reporting (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofNetIncomeorLossandTotalAssetsTable" id="bacq_r_ScheduleofNetIncomeorLossandTotalAssetsTable">    
        <link:definition>996016 - Disclosure - Segment Reporting - Schedule of Net Income or Loss and Total Assets (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofValuationofthePublicRightsTable" id="bacq_r_ScheduleofValuationofthePublicRightsTable">   
        <link:definition>996017 - Disclosure - Summary of Significant Accounting Policies - Schedule of Valuation of the Public Rights (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofOrdinarySharesubjecttoPossibleRedemptionTable" id="bacq_r_ScheduleofOrdinarySharesubjecttoPossibleRedemptionTable"> 
        <link:definition>996018 - Disclosure - Summary of Significant Accounting Policies - Schedule of Ordinary Share subject to Possible Redemption (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofBasicandDilutedNetIncomeTable" id="bacq_r_ScheduleofBasicandDilutedNetIncomeTable">    
        <link:definition>996019 - Disclosure - Summary of Significant Accounting Policies - Schedule of Basic and Diluted Net Income (Details)</link:definition> 
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofCompanysAssetsandLiabilitiesTable0" id="bacq_r_ScheduleofCompanysAssetsandLiabilitiesTable0">    
        <link:definition>996020 - Disclosure - Fair Value Measurements - Schedule of Company&#8217;s Assets and Liabilities (Details)</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/ScheduleofNetIncomeorLossandTotalAssetsTable0" id="bacq_r_ScheduleofNetIncomeorLossandTotalAssetsTable0"> 
        <link:definition>996021 - Disclosure - Segment Reporting - Schedule of Net Income or Loss and Total Assets (Details)</link:definition>   
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
      <link:roleType roleURI="http://www.BleichroederAcquisitionCorp.I.com/role/DocumentAndEntityInformation" id="DocumentAndEntityInformation">     
        <link:definition>000 - Document - Document And Entity Information</link:definition>  
        <link:usedOn>link:presentationLink</link:usedOn>  
        <link:usedOn>link:definitionLink</link:usedOn>     
        <link:usedOn>link:calculationLink</link:usedOn> 
      </link:roleType>   
    </xs:appinfo>   
  </xs:annotation>    
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>  
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>  
  <xs:import namespace="http://fasb.org/us-types/2025" schemaLocation="https://xbrl.fasb.org/us-gaap/2025/elts/us-types-2025.xsd"/>  
  <xs:import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd"/>     
  <xs:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>   
  <xs:import namespace="http://fasb.org/srt-types/2025" schemaLocation="https://xbrl.fasb.org/srt/2025/elts/srt-types-2025.xsd"/>     
  <xs:import namespace="http://xbrl.sec.gov/sic/2025" schemaLocation="https://xbrl.sec.gov/sic/2025/sic-2025.xsd"/> 
  <xs:import namespace="http://xbrl.sec.gov/spac/2025" schemaLocation="https://xbrl.sec.gov/spac/2025/spac-2025.xsd"/>    
  <xs:element name="NetTangibleBookValueMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NetTangibleBookValueMember"/>    
  <xs:element name="AnticipatedTransactionExpensesMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_AnticipatedTransactionExpensesMember"/>    
  <xs:element name="PIPEInvestmentProceedsMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PIPEInvestmentProceedsMember"/>   
  <xs:element name="RedemptionsFromTrustAccountMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_RedemptionsFromTrustAccountMember"/>   
  <xs:element name="SponsorMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_SponsorMember"/>   
  <xs:element name="PIPEInvestorsMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PIPEInvestorsMember"/>     
  <xs:element name="NewMerlinMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NewMerlinMember"/>  
  <xs:element name="InflectionPointMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_InflectionPointMember"/>    
  <xs:element name="UnaffiliatedInflectionPointPublicShareholdersMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnaffiliatedInflectionPointPublicShareholdersMember"/>    
  <xs:element name="ScheduleOfValuationOfThePublicRightsAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfValuationOfThePublicRightsAbstract"/>  
  <xs:element name="ScheduleOfBasicAndDilutedNetIncomePerOrdinaryShareAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfBasicAndDilutedNetIncomePerOrdinaryShareAbstract"/>     
  <xs:element name="ScheduleOfCompanySAssetsAndLiabilitiesAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfCompanySAssetsAndLiabilitiesAbstract"/> 
  <xs:element name="ScheduleOfOrdinaryShareSubjectToPossibleRedemptionAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfOrdinaryShareSubjectToPossibleRedemptionAbstract"/>     
  <xs:element name="ScheduleOfBasicAndDilutedNetIncomeAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfBasicAndDilutedNetIncomeAbstract"/>   
  <xs:element name="ScheduleOfNetIncomeOrLossAndTotalAssetsAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfNetIncomeOrLossAndTotalAssetsAbstract"/>   
  <xs:element name="LiabilitiesClassAOrdinarySharesSubjectToPossibleRedemptionAndShareholdersDeficitAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_LiabilitiesClassAOrdinarySharesSubjectToPossibleRedemptionAndShareholdersDeficitAbstract"/>     
  <xs:element name="LiabilitiesClassAOrdinarySharesSubjectToPossibleRedemptionAndShareholdersDeficitAbstract0" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_LiabilitiesClassAOrdinarySharesSubjectToPossibleRedemptionAndShareholdersDeficitAbstract0"/>  
  <xs:element name="UnlabeledAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnlabeledAbstract"/>   
  <xs:element name="UnlabeledAbstract0" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnlabeledAbstract0"/>     
  <xs:element name="UnlabeledAbstract1" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnlabeledAbstract1"/>     
  <xs:element name="UnlabeledAbstract2" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnlabeledAbstract2"/>     
  <xs:element name="UnlabeledAbstract3" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnlabeledAbstract3"/>     
  <xs:element name="LessAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_LessAbstract"/>   
  <xs:element name="PlusAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PlusAbstract"/>   
  <xs:element name="PlusAbstract0" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PlusAbstract0"/>     
  <xs:element name="PlusAbstract1" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PlusAbstract1"/>     
  <xs:element name="PlusAbstract2" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PlusAbstract2"/>     
  <xs:element name="BasicAndDilutedNetIncomeLossPerOrdinaryShareAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_BasicAndDilutedNetIncomeLossPerOrdinaryShareAbstract"/>   
  <xs:element name="LessAbstract0" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_LessAbstract0"/>     
  <xs:element name="PlusAbstract3" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PlusAbstract3"/>     
  <xs:element name="BasicAndDilutedNetIncomePerShareOfCommonStockAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_BasicAndDilutedNetIncomePerShareOfCommonStockAbstract"/>     
  <xs:element name="NumeratorAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NumeratorAbstract"/>   
  <xs:element name="DenominatorAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_DenominatorAbstract"/>  
  <xs:element name="AssetAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_AssetAbstract"/>     
  <xs:element name="ShortTermPrepaidInsurance" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_ShortTermPrepaidInsurance"/>   
  <xs:element name="AccruedOfferingCostsCurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_AccruedOfferingCostsCurrent"/>   
  <xs:element name="CashUnderwritingFeePayable" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_CashUnderwritingFeePayable"/> 
  <xs:element name="DeferredUnderwritingFeePayableNoncurrent" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_DeferredUnderwritingFeePayableNoncurrent"/>    
  <xs:element name="InterestIncomeOnInvestmentsHeldInTrustAccount" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_InterestIncomeOnInvestmentsHeldInTrustAccount"/>     
  <xs:element name="StockIssuedDuringPeriodValueSaleOfPrivatePlacementUnits" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_StockIssuedDuringPeriodValueSaleOfPrivatePlacementUnits"/>     
  <xs:element name="StockIssuedDuringPeriodSharesSaleOfPrivatePlacementUnits" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_StockIssuedDuringPeriodSharesSaleOfPrivatePlacementUnits"/>  
  <xs:element name="FormationCostsPaidBySponsorInExchangeForIssuanceOfClassBOrdinaryShares" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_FormationCostsPaidBySponsorInExchangeForIssuanceOfClassBOrdinaryShares"/>     
  <xs:element name="PaymentOfOperationCostsThroughPromissoryNote" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_PaymentOfOperationCostsThroughPromissoryNote"/>  
  <xs:element name="FormationCosts" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_FormationCosts"/>  
  <xs:element name="DeferredOfferingCostsIncludedInAccruedOfferingCosts" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_DeferredOfferingCostsIncludedInAccruedOfferingCosts"/>  
  <xs:element name="PrepaidServicesPaidBySponsorThroughThePromissoryNoteRelatedParty" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_PrepaidServicesPaidBySponsorThroughThePromissoryNoteRelatedParty"/>   
  <xs:element name="DeferredUnderwritingFeePayable" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_DeferredUnderwritingFeePayable"/>     
  <xs:element name="InitialPublicOfferingTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_InitialPublicOfferingTextBlock"/> 
  <xs:element name="PrivatePlacementTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PrivatePlacementTextBlock"/> 
  <xs:element name="LiquidityCapitalResourcesAndGoingConcernPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_LiquidityCapitalResourcesAndGoingConcernPolicyTextBlock"/> 
  <xs:element name="EmergingGrowthCompanyPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_EmergingGrowthCompanyPolicyTextBlock"/>   
  <xs:element name="InvestmentsHeldInTrustAccountPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_InvestmentsHeldInTrustAccountPolicyTextBlock"/>    
  <xs:element name="OfferingCostsPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_OfferingCostsPolicyTextBlock"/>  
  <xs:element name="RightsPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_RightsPolicyTextBlock"/>   
  <xs:element name="ClassARedeemableShareClassificationPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ClassARedeemableShareClassificationPolicyTextBlock"/> 
  <xs:element name="LiquidityAndCapitalResourcesPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_LiquidityAndCapitalResourcesPolicyTextBlock"/>  
  <xs:element name="CashHeldInTrustAccountPolicyTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_CashHeldInTrustAccountPolicyTextBlock"/>     
  <xs:element name="ScheduleOfMarketAssumptionsInValuationOfPublicRightsTableTextBlock" type="dtr:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ScheduleOfMarketAssumptionsInValuationOfPublicRightsTableTextBlock"/>   
  <xs:element name="UnderlyingSharePrice" type="dtr:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnderlyingSharePrice"/>     
  <xs:element name="PreadjustedValuePerShareRight" type="dtr:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PreadjustedValuePerShareRight"/>   
  <xs:element name="MarketAdjustment" type="dtr:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_MarketAdjustment"/> 
  <xs:element name="FairValuePerShareRight" type="dtr:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_FairValuePerShareRight"/>    
  <xs:element name="ProceedsAllocatedToPublicRights" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_ProceedsAllocatedToPublicRights"/> 
  <xs:element name="SignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomePerOrdinaryShareDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_SignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomePerOrdinaryShareDetailsTable"/> 
  <xs:element name="FairValueMeasurementsScheduleofCompanysAssetsandLiabilitiesDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_FairValueMeasurementsScheduleofCompanysAssetsandLiabilitiesDetailsTable"/> 
  <xs:element name="SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeDetailsTable"/>  
  <xs:element name="SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeDetailsLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeDetailsLineItems"/>     
  <xs:element name="FairValueMeasurementsScheduleofCompanysAssetsandLiabilitiesDetailsLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_FairValueMeasurementsScheduleofCompanysAssetsandLiabilitiesDetailsLineItems"/>    
  <xs:element name="DescriptionofOrganizationandBusinessOperationsDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_DescriptionofOrganizationandBusinessOperationsDetailsTable"/>     
  <xs:element name="UnitsIssuedDuringPeriodSharesNewIssues" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnitsIssuedDuringPeriodSharesNewIssues"/> 
  <xs:element name="NumberOfSharesIssuedPerUnit" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NumberOfSharesIssuedPerUnit"/>    
  <xs:element name="TransactionCosts" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_TransactionCosts"/> 
  <xs:element name="DeferredUnderwritingFee" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_DeferredUnderwritingFee"/>     
  <xs:element name="PercentageOfRedeemInitialBusinessCombination" type="dtr:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PercentageOfRedeemInitialBusinessCombination"/>  
  <xs:element name="InterestToPayDissolutionExpenses" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_InterestToPayDissolutionExpenses"/>   
  <xs:element name="ConvertiblePromissoryNotes" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_ConvertiblePromissoryNotes"/> 
  <xs:element name="CommonStockPurchasePrice" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_CommonStockPurchasePrice"/>   
  <xs:element name="PercentageOfNumberOfShares" type="dtr:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PercentageOfNumberOfShares"/> 
  <xs:element name="AggregatePurchasePrice" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_AggregatePurchasePrice"/>    
  <xs:element name="InvestmentsMaximumMaturityTerm" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_InvestmentsMaximumMaturityTerm"/>  
  <xs:element name="WorkingCapitalDeficit" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_WorkingCapitalDeficit"/> 
  <xs:element name="WeightedAverageNumberOfSharesForfeited" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_WeightedAverageNumberOfSharesForfeited"/> 
  <xs:element name="InitialPublicOfferingDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_InitialPublicOfferingDetailsTable"/>     
  <xs:element name="PrivatePlacementDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_PrivatePlacementDetailsTable"/>     
  <xs:element name="NumberOfOrdinaryShares" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NumberOfOrdinaryShares"/>    
  <xs:element name="PublicSharesRedemptionPercentage" type="dtr:percentItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item" id="bacq_PublicSharesRedemptionPercentage"/>  
  <xs:element name="RelatedPartyTransactionsDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_RelatedPartyTransactionsDetailsTable"/> 
  <xs:element name="AdditionalSharesIssued" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_AdditionalSharesIssued"/>    
  <xs:element name="PercentageOfIssuedAndOutstandingShares" type="dtr:percentItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item" id="bacq_PercentageOfIssuedAndOutstandingShares"/>    
  <xs:element name="RestrictionsOnTransferPeriodOfTimeAfterBusinessCombinationCompletion" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_RestrictionsOnTransferPeriodOfTimeAfterBusinessCombinationCompletion"/>   
  <xs:element name="NumberOfTradingDays" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NumberOfTradingDays"/>     
  <xs:element name="ThresholdPeriodAfterBusinessCombinationInWhichSpecifiedTradingDaysWithinAnySpecifiedTradingDayPeriodCommences" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_ThresholdPeriodAfterBusinessCombinationInWhichSpecifiedTradingDaysWithinAnySpecifiedTradingDayPeriodCommences"/>     
  <xs:element name="WorkingCapitalLoanAmount" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_WorkingCapitalLoanAmount"/>  
  <xs:element name="WorkingCapitalOutstandingLoans" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item" id="bacq_WorkingCapitalOutstandingLoans"/>    
  <xs:element name="CommitmentsandContingenciesDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_CommitmentsandContingenciesDetailsTable"/>  
  <xs:element name="OverAllotmentOptionPeriod" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_OverAllotmentOptionPeriod"/>  
  <xs:element name="UnderwritingCashDiscountPerUnit" type="dtr:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnderwritingCashDiscountPerUnit"/>  
  <xs:element name="UnderwriterCashDiscount" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnderwriterCashDiscount"/>     
  <xs:element name="DeferredFeePerUnit" type="dtr:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_DeferredFeePerUnit"/> 
  <xs:element name="ShareholdersDeficitDetailsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem" id="bacq_ShareholdersDeficitDetailsTable"/> 
  <xs:element name="AggregateShareIssuedPercentage" type="dtr:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_AggregateShareIssuedPercentage"/>    
  <xs:element name="BusinessCombinationConsiderationsTransferredEquityInterestsIssuedAndIssuable" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item" id="bacq_BusinessCombinationConsiderationsTransferredEquityInterestsIssuedAndIssuable"/> 
  <xs:element name="CommonStockShareIssued" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item" id="bacq_CommonStockShareIssued"/>   
  <xs:element name="CommonStockShareOutstanding" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item" id="bacq_CommonStockShareOutstanding"/>   
  <xs:element name="BusinessCombinationAgreementMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_BusinessCombinationAgreementMember"/>     
  <xs:element name="FounderShareMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_FounderShareMember"/>   
  <xs:element name="FounderShares1Member" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_FounderShares1Member"/>  
  <xs:element name="NewMerlinLabsMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_NewMerlinLabsMember"/>     
  <xs:element name="PostBusinessCombinationMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PostBusinessCombinationMember"/>     
  <xs:element name="PublicShareMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PublicShareMember"/> 
  <xs:element name="PublicSharesMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_PublicSharesMember"/>   
  <xs:element name="SeriesACumulativeConvertiblePreferredStockMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_SeriesACumulativeConvertiblePreferredStockMember"/>   
  <xs:element name="SeriesAPreferredStockInvestmentMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_SeriesAPreferredStockInvestmentMember"/> 
  <xs:element name="UnderwritingAgreementMember" type="dtr:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_UnderwritingAgreementMember"/> 
<!-- [WMV6][MRIW5GKjXKeIHsfwj8JCliX7QB3wecUDm3HfhPGbVItX5C6QpAvAM5aYVTzpXqTsS2Xh+bUyVr5SDVY99lemaipR7YsBH5Z9AMPArZl7dzNgmKEWERGXqK0vPHBECv7vaQHNdyCSKZwK6YvXBBOiAwTHyOrc21FGv4oMJJZNLVEihY/k3mwrtzf/HYMhs9b3p658Wj9qvs2coa0aa7+GomiOCJ2yPa9wSVSlp9iYwyp55PaYUjcGRCafSq6fV7/eLQT45LWjv0RIK7dSp8B53T85w0GOD3XqvkD4JXoNPQ7NkkEWYhyAzaiVCh10L4dgP3FIYJownonP+saFtZT8tZpkmx3TYWQf03tEa5kV5oLXHu/ALyOTA/5NJcniHXTX+fzcpR+Eti6jcMif4xVibAHpf4kWTfkoOpMXMqdcJ030r8qokQM1+DwA0sqFrldDvDk=] CSR-->   
  <xs:element name="DocumentAndEntityInformationAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item" id="bacq_DocumentAndEntityInformationAbstract"/> 
</xs:schema>
