(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
        
)