defpred S₁[ object ] means ex msf being ManySortedFunction of U1,U1 st
( $1 = msf & msf is_isomorphism U1,U1 );
consider X being set such that
A1: for x being object holds
( x in X iff ( x in MSFuncs ( the Sorts of U1, the Sorts of U1) & S₁[x] ) ) from XBOOLE_0:sch 1();
A2: X c= MSFuncs ( the Sorts of U1, the Sorts of U1) by A1;
( id the Sorts of U1 in MSFuncs ( the Sorts of U1, the Sorts of U1) & ex F being ManySortedFunction of U1,U1 st
( id the Sorts of U1 = F & F is_isomorphism U1,U1 ) ) by Th20, MSUALG_3:16;
then reconsider X = X as MSFunctionSet of U1,U1 by A1, A2;
take X ; :: thesis: for h being ManySortedFunction of U1,U1 holds
( h in X iff h is_isomorphism U1,U1 )
let h be ManySortedFunction of U1,U1; :: thesis: ( h in X iff h is_isomorphism U1,U1 )

hereby :: thesis: ( h is_isomorphism U1,U1 implies h in X )

assume h in X ; :: thesis: h is_isomorphism U1,U1
then ex msf being ManySortedFunction of U1,U1 st
( h = msf & msf is_isomorphism U1,U1 ) by A1;
hence h is_isomorphism U1,U1 ; :: thesis: verum

end;

h in MSFuncs ( the Sorts of U1, the Sorts of U1) by Th20;
hence ( h is_isomorphism U1,U1 implies h in X ) by A1; :: thesis: verum