simp [tail, nth]
case hg.mk.intro.refl.refl
α : Type u_1
σ✝ σ : Stream' α
⊢ match
    match (σ, 0) with
    | (σ, 0) => (tail (tail σ), 0)
    | (σ, Nat.succ m) => (tail σ, m) with
  | (σ_1, n) => σ_1 = tail (tail σ) ∧ n = 0
no goals