simp [neg_toUint]
case a
sz sz' : ℕ
H : sz = Nat.succ sz'
h : sz' + 1 > 0
⊢ toUint (-1) ≡ 2 ^ sz' + (2 ^ sz' - 1) [2^sz' + 1]
case a
sz sz' : ℕ
H : sz = Nat.succ sz'
h : sz' + 1 > 0
⊢ mod2 (-toUint 1) (sz' + 1) ≡ 2 ^ sz' + (2 ^ sz' - 1) [2^sz' + 1]