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

theorem
  a <= b implies b = a "\/" (b\a)
proof
  assume
A1: a <= b;
  a "\/" (b\a) = (a"\/"b) "/\" (a"\/"'not' a) by WAYBEL_1:5
    .= b"/\"('not' a"\/"a) by A1,Th8
    .= b"/\"Top L by Th34
    .= b by WAYBEL_1:4;
  hence thesis;
end;
