theorem Th2:
  n1 + n <= n2 + 1 & n > 0 implies n1 <= n2
proof
  assume that
A1: n1 + n <= n2 + 1 and
A2: n > 0;
  1 + 0 <= n by A2,NAT_1:13;
  hence thesis by A1,XREAL_1:8;
end;
