YES
(ignored inputs)COMMENT doi:10.1007/BFb0052357 [21] TRS R_3 submitted by: Takahito Aoto , Junichi Yoshida , and Yoshihito Toyama
Rewrite Rules:
   [ f(?x) -> ?x,
     f(?x) -> f(f(?x)) ]
Apply Direct Methods...
Inner CPs:
   [  ]
Outer CPs:
   [ ?x = f(f(?x)) ]
Overlay, check Innermost Termination...
unknown Innermost Terminating
unknown Knuth & Bendix
Linear
Development Closed
Direct Methods: CR

Combined result: CR
75.trs: Success(CR)
(0 msec.)