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' 'not' b) by Th36
    .= a"/\"('not' a"\/"b) by WAYBEL_1:87
    .= (a"/\"'not' a)"\/"(a"/\"b) by WAYBEL_1:def 3
    .= Bottom L"\/"(a"/\"b) by Th34
    .= a"/\"b by WAYBEL_1:3;
end;
