End Forall.
Section Concat.

(* Specifications: *)
Lemma concat_unary_is_map {A B:Type}: ∀ l (f:A→B),
concat (map (λ x, [f x]) l) = map f l.
Lemma in_concat_const_is_in {A B:Type} (a:A) lfix l:
a ∈ concat (map (λ _ : B, lfix) l) ↔ l ≠ [] ∧ a ∈ lfix.