
theorem Th8:
  for L be sup-Semilattice for a,b be Element of L holds a <= b
  implies a "\/" b = b
proof
  let L be sup-Semilattice;
  let a,b be Element of L;
A1: b <= b;
  assume a <= b;
  then b <= a "\/" b & a "\/" b <= b by A1,YELLOW_0:22;
  hence thesis by YELLOW_0:def 3;
end;
