(VAR x xs y ys zs )
(RULES 
        isEmpty(nil) -> true
        isEmpty(cons(x, xs)) -> false
        last(cons(x, nil)) -> x
        last(cons(x, cons(y, ys))) -> last(cons(y, ys))
        dropLast(nil) -> nil
        dropLast(cons(x, nil)) -> nil
        dropLast(cons(x, cons(y, ys))) -> cons(x, dropLast(cons(y, ys)))
        append(nil, ys) -> ys
        append(cons(x, xs), ys) -> cons(x, append(xs, ys))
        reverse(xs) -> rev(xs, nil)
        rev(xs, ys) -> if(isEmpty(xs), dropLast(xs), append(ys, last(xs)), ys)
        if(true, xs, ys, zs) -> zs
        if(false, xs, ys, zs) -> rev(xs, ys)
        
)