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

theorem
  incl E is faithful
proof
  let a,b be Object of E such that
  Hom(a,b) <> {};
  let f1,f2 be Morphism of a,b;
  (incl E).f1 = f1 by FUNCT_1:18;
  hence thesis by FUNCT_1:18;
end;
