reserve B,C,D for Category;

theorem Th29:
  for S being Contravariant_Functor of C,D,c being Object of C
  holds S.(id c) = id((Obj S).c)
proof
  let S be Contravariant_Functor of C,D,c be Object of C;
  ex d being Object of D st S.(id c) = id d by Def9;
  hence thesis by Th28;
end;
