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