GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
LoadPackage( "ModulePresentationsForCAP" ); LoadPackage( "RingsForHomalg" ); Q := HomalgFieldOfRationalsInSingular( ); R := Q * "x,y"; F := FreeLeftPresentation( 1, R ); alpha1 := PresentationMorphism( F, HomalgMatrix( "[ [ x ] ]", R ), F ); alpha2 := PresentationMorphism( F, HomalgMatrix( "[ [ y ] ]", R ), F ); ## Initializing the deductive system # alpha1 := InDeductiveSystem( alpha1_eval ); # # alpha2 := InDeductiveSystem( alpha2_eval ); ## Formal computation P := FiberProduct( alpha1, alpha2 ); pi1 := ProjectionInFactorOfFiberProduct( [ alpha1, alpha2 ], 1 ); composite := PreCompose( pi1, alpha1 ); PrintHistory( composite ); HasIsMonomorphism( composite ); IsMonomorphism( alpha1 ); IsMonomorphism( alpha2 ); HasEvaluation( composite ); HasIsMonomorphism( composite ); IsMonomorphism( composite ); HasEvaluation( composite ); Evaluation( composite ); HasEvaluation( composite );