reserve L for Boolean non empty RelStr;
reserve a,b,c,d for Element of L;

theorem
  (a"\/"b)\b = a\b
proof
  thus (a"\/"b)\b = (a"\/"b)"/\"'not' b
    .= (a"/\"'not' b)"\/"(b"/\"'not' b) by WAYBEL_1:def 3
    .= (a"/\"'not' b)"\/"Bottom L by Th34
    .= a\b by WAYBEL_1:3;
end;
