(VAR x)
(RULES
a(a(x)) -> b(b(b(x))) 
a(x) -> c(d(x)) 
b(b(x))  -> c(c(c(x))) 
c(c(x))  -> d(d(d(x))) 
e(d(x)) -> a(b(c(d(e(x)))))
b(x) -> d(d(x)) 
e(c(x)) -> b(a(a(e(x)))) 
c(d(d(x)))  -> a(x)
)