(VAR x y z )
(RULES 
        bsort(nil) -> nil
        bsort(.(x, y)) -> last(.(bubble(.(x, y)), bsort(butlast(bubble(.(x, y))))))
        bubble(nil) -> nil
        bubble(.(x, nil)) -> .(x, nil)
        bubble(.(x, .(y, z))) -> if(<=(x, y), .(y, bubble(.(x, z))), .(x, bubble(.(y, z))))
        last(nil) -> 0
        last(.(x, nil)) -> x
        last(.(x, .(y, z))) -> last(.(y, z))
        butlast(nil) -> nil
        butlast(.(x, nil)) -> nil
        butlast(.(x, .(y, z))) -> .(x, butlast(.(y, z)))
        
)