theorem knockout_cascade {N : ℕ} (hN : 0 < N) (F : Fin N → ℝ)
(hF0 : F ⟨0, hN⟩ = 0)
(hdep : ∀ (i : ℕ) (hi : i < N), 0 < i →
∃ (a : ℝ), F ⟨i, hi⟩ = a * F ⟨i - 1, by omega⟩)
: ∀ (i : ℕ) (hi : i < N), F ⟨i, hi⟩ = 0 := by
intro i hi
induction i with
| zero => convert hF0
| succ k ih =>
obtain ⟨a, ha⟩ := hdep (k + 1) hi (by omega)
rw [ha]
have : k + 1 - 1 = k := by omega
simp only [this]
rw [ih (by omega), mul_zero]Theorems 7-8, Propositions 5 and 7, Corollary 3: