(VAR x y)
(RULES
random(x) -> rand(x, 0)
rand(x, y) -> y :|: x = 0
rand(x, y) -> rand(x - 1, id_inc(y)) :|: x > 0
rand(x, y) -> rand(x + 1, id_dec(y)) :|: 0 > x
id_inc(x) -> x
id_inc(x) -> x + 1
id_dec(x) -> x
id_dec(x) -> x - 1
)