NO
(ignored inputs)COMMENT Example 6.2.7 of \cite{BN98}
Rewrite Rules:
   [ f(f(?x)) -> g(?x) ]
Apply Direct Methods...
Inner CPs:
   [ f(g(?x)) = g(f(?x)) ]
Outer CPs:
   [  ]
not Overlay, check Termination...
Terminating, not WCR
Knuth & Bendix
Direct Methods: not CR

Final result: not CR
7.trs: Success(not CR)
(0 msec.)