theorem
  F[;](d,T9) = F[;](d,id D9)*T9
proof
  rng T9 c= D9;
  hence F[;](d,T9) = F[;](d,(id D9)*T9) by RELAT_1:53
    .= F[;](d,(id D9))*T9 by FUNCOP_1:34;
end;
