(from Ste92 example 1)
(VAR x  y  z)
(RULES
f(cons(nil,y)) -> y
f(cons(f(cons(nil,y)), z)) -> copy(n, y, z)
copy(0, y, z) -> f(z)
copy(s(x), y, z) -> copy(x, y, cons(f(y), z))
)