Section EXTRA1.
Definition inconsistent {L : language} (Gamma : ensemble (frm L)) : Prop :=
forall p, Gamma ⊢ p.
Context {L : language}.

Lemma ExistentialI (Gamma : ensemble (frm L)) x t A
(INFERS1 : Gamma ⊢ subst_frm (one_subst x t) A)
: Gamma ⊢ Exs_frm x A.