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