(VAR X Z Y X1 X2) (RULES a__from(X) -> cons(mark(X),from(s(X))) a__first(0,Z) -> nil a__first(s(X),cons(Y,Z)) -> cons(mark(Y),first(X,Z)) a__sel(0,cons(X,Z)) -> mark(X) a__sel(s(X),cons(Y,Z)) -> a__sel(mark(X),mark(Z)) mark(from(X)) -> a__from(mark(X)) mark(first(X1,X2)) -> a__first(mark(X1),mark(X2)) mark(sel(X1,X2)) -> a__sel(mark(X1),mark(X2)) mark(cons(X1,X2)) -> cons(mark(X1),X2) mark(s(X)) -> s(mark(X)) mark(0) -> 0 mark(nil) -> nil a__from(X) -> from(X) a__first(X1,X2) -> first(X1,X2) a__sel(X1,X2) -> sel(X1,X2) )