MAYBE
Input TRS:
      1: a(a(x1)) -> b(b(x1))
      2: c(c(b(x1))) -> d(c(a(x1)))
      3: a(x1) -> d(c(c(x1)))
      4: c(d(x1)) -> b(c(x1))
Number of strict rules: 4
Direct POLO(bPol) ... failed.
Uncurrying ... failed.
Dependency Pairs:
     #1: #c(c(b(x1))) -> #c(a(x1))
     #2: #c(c(b(x1))) -> #a(x1)
     #3: #a(x1) -> #c(c(x1))
     #4: #a(x1) -> #c(x1)
     #5: #c(d(x1)) -> #c(x1)
Number of SCCs: 1, DPs: 5
  SCC { #1..5 }
POLO(Sum)... POLO(max)... QLPOS... POLO(mSum)... QWPOpS(mSum)... Mat2b... failed.
Finding a loop...  failed.