(VAR X XS N X1 X2) (RULES a__from(X) -> cons(mark(X),from(s(X))) a__after(0,XS) -> mark(XS) a__after(s(N),cons(X,XS)) -> a__after(mark(N),mark(XS)) mark(from(X)) -> a__from(mark(X)) mark(after(X1,X2)) -> a__after(mark(X1),mark(X2)) mark(cons(X1,X2)) -> cons(mark(X1),X2) mark(s(X)) -> s(mark(X)) mark(0) -> 0 a__from(X) -> from(X) a__after(X1,X2) -> after(X1,X2) )