f(x,e()) -> x
f(b(),b()) -> e()
f(b(),i(a())) -> f(a(),b())
f(x,i(x)) -> e()
f(f(x,y),z) -> f(x,f(y,z))
f(b(),f(i(a()),x)) -> f(a(),f(b(),x))
i(b()) -> b()
i(e()) -> e()
f(i(x),x) -> e()
f(e(),x) -> x
i(i(x)) -> x
f(i(x),f(x,y)) -> y
f(b(),a()) -> f(i(a()),b())
f(b(),f(a(),x)) -> f(i(a()),f(b(),x))
f(b(),f(b(),x)) -> x
f(x,f(i(x),y)) -> y
i(f(x,y)) -> f(i(y),i(x))
f(a(),f(a(),f(a(),a()))) -> f(i(a()),f(i(a()),f(i(a()),i(a()))))
f(a(),f(a(),f(a(),f(a(),f(a(),x))))) -> f(i(a()),f(i(a()),f(i(a()),x)))
f(i(a()),f(i(a()),f(i(a()),f(i(a()),x)))) -> f(a(),f(a(),f(a(),f(a(),x))))