
theorem Th18:
  for K, L being non empty ComplStr, x being Element of K, y being
  Element of L st the Compl of K = the Compl of L & x = y holds x` = y`
proof
  let K, L be non empty ComplStr, x be Element of K, y be Element of L;
  assume the Compl of K = the Compl of L & x = y;
  then x` = (the Compl of L).y by ROBBINS1:def 3
    .= y` by ROBBINS1:def 3;
  hence thesis;
end;
