(from AG01 4.19)
(VAR x y z)
(RULES
f(x,c(x),c(y)) -> f(y,y,f(y,x,y))
f(s(x),y,z) -> f(x,s(c(y)),c(z))
f(c(x),x,y) -> c(y)
g(x,y) -> x
g(x,y) -> y
)