MAYBE

Problem:
 active(f(a(),b(),X)) -> mark(f(X,X,X))
 active(c()) -> mark(a())
 active(c()) -> mark(b())
 mark(f(X1,X2,X3)) -> active(f(mark(X1),X2,mark(X3)))
 mark(a()) -> active(a())
 mark(b()) -> active(b())
 mark(c()) -> active(c())
 f(mark(X1),X2,X3) -> f(X1,X2,X3)
 f(X1,mark(X2),X3) -> f(X1,X2,X3)
 f(X1,X2,mark(X3)) -> f(X1,X2,X3)
 f(active(X1),X2,X3) -> f(X1,X2,X3)
 f(X1,active(X2),X3) -> f(X1,X2,X3)
 f(X1,X2,active(X3)) -> f(X1,X2,X3)

Proof:
 DP Processor:
  DPs:
   active#(f(a(),b(),X)) -> f#(X,X,X)
   active#(f(a(),b(),X)) -> mark#(f(X,X,X))
   active#(c()) -> mark#(a())
   active#(c()) -> mark#(b())
   mark#(f(X1,X2,X3)) -> mark#(X3)
   mark#(f(X1,X2,X3)) -> mark#(X1)
   mark#(f(X1,X2,X3)) -> f#(mark(X1),X2,mark(X3))
   mark#(f(X1,X2,X3)) -> active#(f(mark(X1),X2,mark(X3)))
   mark#(a()) -> active#(a())
   mark#(b()) -> active#(b())
   mark#(c()) -> active#(c())
   f#(mark(X1),X2,X3) -> f#(X1,X2,X3)
   f#(X1,mark(X2),X3) -> f#(X1,X2,X3)
   f#(X1,X2,mark(X3)) -> f#(X1,X2,X3)
   f#(active(X1),X2,X3) -> f#(X1,X2,X3)
   f#(X1,active(X2),X3) -> f#(X1,X2,X3)
   f#(X1,X2,active(X3)) -> f#(X1,X2,X3)
  TRS:
   active(f(a(),b(),X)) -> mark(f(X,X,X))
   active(c()) -> mark(a())
   active(c()) -> mark(b())
   mark(f(X1,X2,X3)) -> active(f(mark(X1),X2,mark(X3)))
   mark(a()) -> active(a())
   mark(b()) -> active(b())
   mark(c()) -> active(c())
   f(mark(X1),X2,X3) -> f(X1,X2,X3)
   f(X1,mark(X2),X3) -> f(X1,X2,X3)
   f(X1,X2,mark(X3)) -> f(X1,X2,X3)
   f(active(X1),X2,X3) -> f(X1,X2,X3)
   f(X1,active(X2),X3) -> f(X1,X2,X3)
   f(X1,X2,active(X3)) -> f(X1,X2,X3)
  Open