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

theorem
  a\a"/\"b = a\b
proof
  thus a\a"/\"b = a"/\"('not' a"\/"'not' b) by Th36
    .= (a"/\"'not' a)"\/"(a"/\"'not' b) by WAYBEL_1:def 3
    .= Bottom L "\/"(a"/\"'not' b) by Th34
    .= a\b by WAYBEL_1:3;
end;
