theorem Th27:
  f tolerates g +* h implies f tolerates h
proof
  assume
A1: f tolerates g +* h;
  let x be object;
  assume
A2: x in dom f /\ dom h;
  then
A3: x in dom f by XBOOLE_0:def 4;
A4: x in dom h by A2,XBOOLE_0:def 4;
  then x in dom(g +* h) by Th12;
  then
A5: x in dom f /\ dom(g +* h) by A3,XBOOLE_0:def 4;
  (g +* h).x = h.x by A4,Th13;
  hence thesis by A1,A5;
end;
