
theorem Th12:
  Catalan 2 = 1
proof
A1: 4 -' 2 = 4 - 2 by XREAL_1:233
    .= 2;
  2 -' 1 = 2 - 1 by XREAL_1:233
    .= 1;
  then Catalan 2 = 2 / 2 by A1,NEWTON:23
    .= 1;
  hence thesis;
end;
