(=> (bor $x (bor $x $y))
    (bor $x $y))

(=> (bor $y (bor $x $y))
    (bor $x $y))

(=> (bor (bor $x $y) $x)
    (bor $x $y))

(=> (bor (bor $x $y) $y)
    (bor $x $y))