theorem
  (g-h) (/) c = g(/)c - h(/)c
proof
A1: dom((g-h)(/)c) = dom(g-h) by VALUED_1:def 5;
A2: dom(g-h) = dom g /\ dom h by VALUED_1:12;
  dom(g(/)c) = dom g & dom(h(/)c) = dom h by VALUED_1:def 5;
  hence
A3: dom((g-h)(/)c) = dom(g(/)c-h(/)c) by A1,A2,VALUED_1:12;
  let x be object;
  assume
A4: x in dom((g-h)(/)c);
  thus ((g-h)(/)c).x = (g-h).x * c" by VALUED_1:6
    .= (g.x-h.x)*c" by A1,A4,VALUED_1:13
    .= g.x*c" - h.x*c"
    .= (g(/)c).x - h.x*c" by VALUED_1:6
    .= (g(/)c).x - (h(/)c).x by VALUED_1:6
    .= (g(/)c-h(/)c).x by A3,A4,VALUED_1:13;
end;
