(VAR X Y Z X1 X2) (RULES active(f(X)) -> mark(cons(X,f(g(X)))) active(g(0)) -> mark(s(0)) active(g(s(X))) -> mark(s(s(g(X)))) active(sel(0,cons(X,Y))) -> mark(X) active(sel(s(X),cons(Y,Z))) -> mark(sel(X,Z)) active(f(X)) -> f(active(X)) active(cons(X1,X2)) -> cons(active(X1),X2) active(g(X)) -> g(active(X)) active(s(X)) -> s(active(X)) active(sel(X1,X2)) -> sel(active(X1),X2) active(sel(X1,X2)) -> sel(X1,active(X2)) f(mark(X)) -> mark(f(X)) cons(mark(X1),X2) -> mark(cons(X1,X2)) g(mark(X)) -> mark(g(X)) s(mark(X)) -> mark(s(X)) sel(mark(X1),X2) -> mark(sel(X1,X2)) sel(X1,mark(X2)) -> mark(sel(X1,X2)) proper(f(X)) -> f(proper(X)) proper(cons(X1,X2)) -> cons(proper(X1),proper(X2)) proper(g(X)) -> g(proper(X)) proper(0) -> ok(0) proper(s(X)) -> s(proper(X)) proper(sel(X1,X2)) -> sel(proper(X1),proper(X2)) f(ok(X)) -> ok(f(X)) cons(ok(X1),ok(X2)) -> ok(cons(X1,X2)) g(ok(X)) -> ok(g(X)) s(ok(X)) -> ok(s(X)) sel(ok(X1),ok(X2)) -> ok(sel(X1,X2)) top(mark(X)) -> top(proper(X)) top(ok(X)) -> top(active(X)) )