∀ {α : Type u} {L₁ L₂ L₃ : List (α × Bool)},
  FreeGroup.IsCyclicallyReduced L₂ →
    FreeGroup.IsReduced (L₁ ++ L₂ ++ L₃) →
      ∀ {n : ℕ}, n ≠ 0 → FreeGroup.IsReduced (L₁ ++ (List.replicate n L₂).flatten ++ L₃)