constructor
case h.succ
n : ℕ
h1 :
  (match n.succ % 10 :: digits 10 (n.succ / 10) with
      | [] => default
      | a :: tail => a) =
      6 ∧
    ofDigits 10 (digits 10 (n.succ / 10) ++ [6]) = 4 * (n + 1)
⊢ ProblemPredicate' ((n + 1) / 10) (n + 1)
case h.succ.left
n : ℕ
h1 :
  (match n.succ % 10 :: digits 10 (n.succ / 10) with
      | [] => default
      | a :: tail => a) =
      6 ∧
    ofDigits 10 (digits 10 (n.succ / 10) ++ [6]) = 4 * (n + 1)
⊢ n + 1 = 10 * ((n + 1) / 10) + 6

case h.succ.right
n : ℕ
h1 :
  (match n.succ % 10 :: digits 10 (n.succ / 10) with
      | [] => default
      | a :: tail => a) =
      6 ∧
    ofDigits 10 (digits 10 (n.succ / 10) ++ [6]) = 4 * (n + 1)
⊢ 6 * 10 ^ (digits 10 ((n + 1) / 10)).length + (n + 1) / 10 = 4 * (n + 1)