(VAR x1 )
(RULES 
        a(a(x1)) -> a(b(a(b(a(x1)))))
        c(a(x1)) -> a(b(a(a(c(x1)))))
        b(b(b(x1))) -> a(b(x1))
        c(b(x1)) -> a(a(c(x1)))
        c(b(x1)) -> b(a(d(x1)))
        d(d(x1)) -> d(b(d(b(d(x1)))))
        c(c(x1)) -> c(d(c(x1)))
        a(a(a(x1))) -> a(b(b(x1)))
        
)