theorem
  (A /\ B)^Fob c= (A^Fob) /\ (B^Fob)
proof
  let x be object;
  assume
A1: x in (A /\ B)^Fob;
  (A /\ B)^Fob c= A^Fob & (B /\ A)^Fob c= B^Fob by Th24,XBOOLE_1:17;
  hence thesis by A1,XBOOLE_0:def 4;
end;
