∀ {α : Type u_1} {i : ℕ} {xs : List α} {x : α} {s : ℕ} [inst : BEq α] (h : i < (List.idxsOf x xs s).length),
  (List.findIdxs (fun x_1 => x_1 == x) xs)[i] + 1 ≤ xs.length → (List.findIdxs (fun x_1 => x_1 == x) xs)[i] < xs.length