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(*         *   The Coq Proof Assistant / The Coq Development Team       *)
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(** This module states the axiom of (dependent) functional extensionality and (dependent) eta-expansion. It introduces a tactic [extensionality] to apply the axiom of extensionality to an equality goal. *)
(** The converse of functional extensionality. *)
(** Statements of functional extensionality for simple and dependent functions. *)

Lemma functional_extensionality {A B} (f g : A -> B) :
(forall x, f x = g x) -> f = g.