reserve B,C,D,C9,D9 for Category;

theorem
  for c being Object of C, b being Object of B holds (Obj (B --> c)).b = c
proof
  let c be Object of C, b be Object of B;
  (B --> c).(id b) = id c by FUNCOP_1:7;
  hence thesis by CAT_1:67;
end;
