NO
Rewrite Rules:
   [ len(nil) -> 0,
     len(cons(?x,?xs)) -> s(len(?xs)),
     qrev(nil,?ys) -> ?ys,
     qrev(cons(?x,?xs),?ys) -> qrev(?xs,cons(?x,?ys)),
     +(0,?y) -> ?y,
     +(s(?x),?y) -> s(+(?x,?y)),
     len(qrev(?xs,?ys)) -> +(len(?xs),len(?ys)) ]
Apply Direct Methods...
Inner CPs:
   [ len(?ys_1) = +(len(nil),len(?ys_1)),
     len(qrev(?xs_2,cons(?x_2,?ys_2))) = +(len(cons(?x_2,?xs_2)),len(?ys_2)) ]
Outer CPs:
   [  ]
not Overlay, check Termination...
Terminating, not WCR
Knuth & Bendix
Direct Methods: not CR

Final result: not CR
new/len-qrev.trs: Success(not CR)
(19 msec.)