(VAR w x y )
(RULES 
        f(x, y, w, w, a) -> g1(x, x, y, w)
        f(x, y, w, a, a) -> g1(y, x, x, w)
        f(x, y, a, a, w) -> g2(x, y, y, w)
        f(x, y, a, w, w) -> g2(y, y, x, w)
        g1(x, x, y, a) -> h(x, y)
        g1(y, x, x, a) -> h(x, y)
        g2(x, y, y, a) -> h(x, y)
        g2(y, y, x, a) -> h(x, y)
        h(x, x) -> x
        
)