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