
theorem Th20: :: 4.24
  for L being join-commutative join-associative Huntington non
  empty ComplLLattStr, a, b being Element of L holds a + (a *' b) = a
proof
  let L be join-commutative join-associative Huntington non empty
  ComplLLattStr, a,b be Element of L;
  thus a + (a *' b) = (a *' b) + ((a *' b) + (a *' b`)) by Def6
    .= (a *' b) + (a *' b) + (a *' b`) by LATTICES:def 5
    .= (a *' b) + (a *' b`) by Def7
    .= a by Def6;
end;
