exact Nat.eq_add_of_sub_eq (h.2 (Fin.coe_sub_iff_le.mp rfl)) rfl
case tail.tail.head
d : ℕ
inst✝ : NeZero d
w : Weight 2 d
h : normalized w
⊢ w { val := 2, isLt := (_ : (fun a => (fun a => a < Nat.succ 2) a) 2) } =
    of_fraction d (w 2 - w 1) (w 1) { val := 2, isLt := (_ : (fun a => (fun a => a < Nat.succ 2) a) 2) }
no goals