
theorem Th6:
  for L being join-commutative non empty \/-SemiLattStr, a, b
  being Element of L holds a [= b & b [= a implies a=b
proof
  let L be join-commutative non empty \/-SemiLattStr, a, b be Element of L;
  assume a"\/"b = b & b"\/"a =a;
  hence thesis;
end;
