(VAR X Y X1 X2 X3)
(RULES 
active(f(X,g(X),Y)) -> mark(f(Y,Y,Y))
active(g(b)) -> mark(c)
active(b) -> mark(c)
mark(f(X1,X2,X3)) -> active(f(X1,X2,X3))
mark(g(X)) -> active(g(mark(X)))
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)
g(mark(X)) -> g(X)
g(active(X)) -> g(X)
)