
theorem Th21: :: 4.25
  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` + (a` *' b`)``)` by Th17
    .= (a` + (a` *' b`))` by Th3
    .= a`` by Th20
    .= a by Th3;
end;
