MAYBE

'Pop* (timeout of 60.0 seconds)'
--------------------------------
Answer:           MAYBE
Input Problem:    innermost runtime-complexity with respect to
  Rules:
    {  a(d(x)) -> d(c(b(a(x))))
     , b(c(x)) -> c(d(a(b(x))))
     , a(c(x)) -> x
     , b(d(x)) -> x}

Proof Output:    
  The input cannot be shown compatible