(VAR X Y Z X1 X2) (RULES a__f(X) -> cons(mark(X),f(g(X))) a__g(0) -> s(0) a__g(s(X)) -> s(s(a__g(mark(X)))) a__sel(0,cons(X,Y)) -> mark(X) a__sel(s(X),cons(Y,Z)) -> a__sel(mark(X),mark(Z)) mark(f(X)) -> a__f(mark(X)) mark(g(X)) -> a__g(mark(X)) mark(sel(X1,X2)) -> a__sel(mark(X1),mark(X2)) mark(cons(X1,X2)) -> cons(mark(X1),X2) mark(0) -> 0 mark(s(X)) -> s(mark(X)) a__f(X) -> f(X) a__g(X) -> g(X) a__sel(X1,X2) -> sel(X1,X2) )