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

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