YES
input TRS:
   [ a -> a,
     f(f(?x,b),?y) -> f(?y,b),
     f(b,?y) -> f(?y,b),
     f(?x,a) -> b ]
Try persistent and layer-preserving decomposition...
Sort Assignment:
 a : =>10
 b : =>10
 f : 10*10=>10
maximal types: {10}
...decomposition failed.
TRS:
   [ a -> a,
     f(f(?x,b),?y) -> f(?y,b),
     f(b,?y) -> f(?y,b),
     f(?x,a) -> b ]
unknown Non-Omega-Overlapping
unknown Right-Reducible
Check distinct normal forms in critical pair closure...failed
Obtained TRSs:
   [ a -> a,
     f(f(?x,b),?y) -> f(?y,b),
     f(b,?y) -> f(?y,b),
     f(?x,a) -> b,
     f(a,b) -> b ]
...linear strongly closed TRS
UNC Completion (General)
problems/ex6.trs: Success(UNC)
(0 msec.)