YES
(ignored inputs)COMMENT Example 3 of \cite{Tiw02}
Rewrite Rules:
   [ f(a) -> f(f(a)),
     f(?x) -> f(a) ]
Apply Direct Methods...
Inner CPs:
   [  ]
Outer CPs:
   [ f(f(a)) = f(a) ]
Overlay, check Innermost Termination...
unknown Innermost Terminating
unknown Knuth & Bendix
Linear
Development Closed
Direct Methods: CR

Final result: CR
82.trs: Success(CR)
(0 msec.)