(VAR x y)
(RULES
g(x,x) -> g(a,b)
g(c,g(c,x)) -> g(e,g(d,x))
g(d,g(d,x)) -> g(c,g(e,x))
g(e,g(e,x)) -> g(d,g(c,x))
f(g(x,y)) -> g(y,g(f(f(x)),a))
)