exact match i with
| 0 => by simp [getF]
| j+1 => by simp [rangeF, getF, ih]
case succ
m : ℕ
ih : ∀ (i : ℕ) (h : i < length (rangeF m)), getF (rangeF m) i h = { val := i, isLt := (_ : i < m) }
i : ℕ
⊢ ∀ (h : i < length (rangeF (Nat.succ m))), getF (rangeF (Nat.succ m)) i h = { val := i, isLt := (_ : i < Nat.succ m) }
no goals