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