theorem Th18:
  for f1,f2 being complex-valued Function holds r(#)(f1(#)f2) = f1(#)(r(#)f2)
proof
  let f1,f2 be complex-valued Function;
  thus
A1: dom (r(#)(f1 (#) f2)) = dom (f1 (#) f2) by VALUED_1:def 5
    .= dom f1 /\ dom f2 by VALUED_1:def 4
    .= dom f1 /\ dom (r(#)f2) by VALUED_1:def 5
    .= dom (f1(#)(r(#)f2)) by VALUED_1:def 4;
    let c be object;
    assume
A2: c in dom (r(#)(f1(#)f2));
    then
A3: c in dom (f1(#)f2) by VALUED_1:def 5;
    c in dom f1 /\ dom (r(#)f2) by A1,A2,VALUED_1:def 4;
    then
A4: c in dom (r(#)f2) by XBOOLE_0:def 4;
    thus (r(#)(f1(#)f2)).c = r * ((f1(#)f2).c) by A2,VALUED_1:def 5
      .= r * (((f1.c)) * ((f2.c))) by A3,VALUED_1:def 4
      .= ((f1.c)) * (r * ((f2.c)))
      .= ((f1.c)) * ((r(#)f2).c) by A4,VALUED_1:def 5
      .= (f1(#)(r(#)f2)).c by A1,A2,VALUED_1:def 4;
end;
