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  <xsd:element id="istr_EBPAutomaticEnrollmentMaxPercentagePerEmployee" name="EBPAutomaticEnrollmentMaxPercentagePerEmployee" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:percentItemType" xbrli:periodType="duration"/>
  <xsd:element id="istr_EBPAwardVestingPercentageAfterSixYearsOfServices" name="EBPAwardVestingPercentageAfterSixYearsOfServices" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:percentItemType" xbrli:periodType="instant"/>
  <xsd:element id="istr_EBPAwardVestingPeriod" name="EBPAwardVestingPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration"/>
  <xsd:element id="istr_EBPMaximumOfVestedValueOfParticipantsAccountsRequiredToMakeLumpSumCashPayments" name="EBPMaximumOfVestedValueOfParticipantsAccountsRequiredToMakeLumpSumCashPayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant"/>
  <xsd:element id="istr_EBPMinimumAgeForVoluntaryCatchupContributions" name="EBPMinimumAgeForVoluntaryCatchupContributions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant"/>
  <xsd:element id="istr_EBPNoteReceivableFromParticipantTerm" name="EBPNoteReceivableFromParticipantTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration"/>
  <xsd:element id="istr_EBPVestingPercentagePerYear" name="EBPVestingPercentagePerYear" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:percentItemType" xbrli:periodType="instant"/>
  <xsd:element id="istr_EmployeeBenefitPlanCreditingInterestRate" name="EmployeeBenefitPlanCreditingInterestRate" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:percentItemType" xbrli:periodType="instant"/>
  <xsd:element id="istr_EmployeeBenefitPlanTerminationPlanVestingOnTermination" name="EmployeeBenefitPlanTerminationPlanVestingOnTermination" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:percentItemType" xbrli:periodType="instant"/>
  <xsd:element abstract="true" id="istr_NonPooledAccountsMember" name="NonPooledAccountsMember" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_NoteToFinancialStatementDetailsTextual" name="NoteToFinancialStatementDetailsTextual" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_NotesToFinancialStatements" name="NotesToFinancialStatements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_NotesToFinancialStatementsAbstract" name="NotesToFinancialStatementsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_PolicyTable" name="PolicyTable" nillable="true" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element id="istr_ScheduleOfAssetsTextBlock" name="ScheduleOfAssetsTextBlock" nillable="true" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-note-10-reconciliation-of-financial-statements-to-form-5500-reconciliation-of-net-assets-available-for-benefits-details" name="statement-statement-note-10-reconciliation-of-financial-statements-to-form-5500-reconciliation-of-net-assets-available-for-benefits-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-note-10-reconciliation-of-financial-statements-to-form-5500-reconciliation-of-net-assets-available-for-benefits-detailsC281589C-BA7C-4E80-84AA-6E60CAC63BFE" name="statement-statement-note-10-reconciliation-of-financial-statements-to-form-5500-reconciliation-of-net-assets-available-for-benefits-detailsC281589C-BA7C-4E80-84AA-6E60CAC63BFE" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-note-10-reconciliation-of-financial-statements-to-form-5500-tables" name="statement-statement-note-10-reconciliation-of-financial-statements-to-form-5500-tables" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-note-5-fair-value-measurements-schedule-of-plans-assets-details" name="statement-statement-note-5-fair-value-measurements-schedule-of-plans-assets-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-note-5-fair-value-measurements-schedule-of-plans-assets-detailsBBD3EC28-8367-43C5-AADC-6FA9125B6FC4" name="statement-statement-note-5-fair-value-measurements-schedule-of-plans-assets-detailsBBD3EC28-8367-43C5-AADC-6FA9125B6FC4" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-note-5-fair-value-measurements-tables" name="statement-statement-note-5-fair-value-measurements-tables" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-schedule-h-line-4i-schedule-of-assets-2-details" name="statement-statement-schedule-h-line-4i-schedule-of-assets-2-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-schedule-h-line-4i-schedule-of-assets-details" name="statement-statement-schedule-h-line-4i-schedule-of-assets-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-schedule-h-line-4i-schedule-of-assets-tables" name="statement-statement-schedule-h-line-4i-schedule-of-assets-tables" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="istr_statement-statement-significant-accounting-policies-policies" name="statement-statement-significant-accounting-policies-policies" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
</xsd:schema>
