TRS:
 {   d(x) -> e(u(x)),
  d(u(x)) -> c(x),
  c(u(x)) -> b(x),
  v(e(x)) -> x,
  b(u(x)) -> a(e(x))}
 POP*:
  Precedence:
  b > e, 
  b > a, 
  d > e, 
  d > u, 
  d > c, 
  c > b
  empty
  
Normal:
   pi(d) = [1]
  
Safe:
   pi(a) = [1], pi(b) = [1], pi(c) = [1], pi(u) = [1], pi(e) = [1]
  
Predicative System:
   {    d(x;) -> e(;u(;x)),
    d(u(;x);) -> c(;x),
    c(;u(;x)) -> b(;x),
    v(e(;x);) -> x,
    b(;u(;x)) -> a(;e(;x))}
  Qed