cases br <;> simp at h' <;> simp [toSint, h'] <;> sorry_arith
sz : ℕ
n' m' : FinInt sz
br : Bool
r : FinInt sz
h : addfull n' m' = next br r
h' : toUint (next br r) = toUint n' + toUint m'
⊢ toSint
      (match next br r with
      | next false r => next true (next false r)
      | next true r => next true (next true r)) =
    toSint (next true n') + toSint (next true m')
no goals