reserve B,C,D,C9,D9 for Category;
reserve E for Subcategory of C;

theorem Th39:
  for T being Functor of C,D, T9 being Functor of C9,D9 holds [:T,
  T9:] = <:T*pr1(C,C9),T9*pr2(C,C9):>
proof
  let T be Functor of C,D, T9 be Functor of C9,D9;
  dom T = the carrier' of C & dom T9 = the carrier' of C9 by FUNCT_2:def 1;
  hence thesis by FUNCT_3:66;
end;
