YES
af/ONE-SORTED/36.trs
Input rules:
   [ f(a) -> f(f(a)),
     a -> b,
     f(?x:o) -> f(b) ]
Sorts having no ground terms: 
Rules applicable to ground terms:
   [ f(a) -> f(f(a)),
     a -> b,
     f(?x:o) -> f(b) ]
Constructor pattern: [f(?x_1),b]
Defined pattern: [a]
Constructor subsystem:
   [ f(?x) -> f(b) ]
f(?x) -> f(b)
{?x:=b}
   [ {?x:=f(?x_1)} ]
Modified Constructor subsystem:
   [ f(f(?x_1)) -> f(b) ]
candidate for a:
   [ a -> b ]
Find a quasi-ordering ...
order successfully found
Precedence:
 f : Mul;
 a : Mul;
 b : Mul;
Rules:
   [ a -> b,
     f(f(?x_1)) -> f(b) ]
Check confluence of constructor subsystem...
Check Termination...
Terminating, WCR: CR
Conjectures:
   [ f(a) = f(f(a)) ]
STEP 0
ES:
   [ f(a) = f(f(a)) ]
HS:
   [ ]
ES0:
   [ f(b) = f(b) ]
HS0:
   [ ]
ES1:
   [ ]
HS1:
   [ ]
: Success(GCR)
(2 msec.)
0.02