
theorem Th4:
  for A,B being transitive with_units non empty AltCatStr, F
being Functor of A,B holds for a being Object of A holds (idt F)!a =
  idm(F.a)
proof
  let A,B be transitive with_units non empty AltCatStr, F be
  Functor of A,B;
  let a be Object of A;
  thus (idt F)!a = (idt F qua ManySortedSet of the carrier of A).a by Def4
    .= idm (F.a) by Def3;
end;
