∀[T:Type]. ∀[l:T List]. uiff(||l|| = 0 ∈ ℤ;l = [] ∈ (T List))
{ (Auto THEN DVar `l' THEN All Reduce THEN Auto) }
1. T : Type
2. u : T
3. v : T List
4. (||v|| + 1) = 0 ∈ ℤ
⊢ [u / v] = [] ∈ (T List)