YES
(ignored inputs)COMMENT Example 3.5.7 of \cite{Gra96thesis}
Rewrite Rules:
   [ f(?x) -> g(k(?x)),
     f(?x) -> a,
     g(?x) -> a,
     k(a) -> k(k(a)) ]
Apply Direct Methods...
Inner CPs:
   [  ]
Outer CPs:
   [ g(k(?x)) = a ]
Overlay, check Innermost Termination...
unknown Innermost Terminating
unknown Knuth & Bendix
Linear
Development Closed
Direct Methods: CR

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