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

Lemma DisjunctionI2 (Gamma : ensemble (frm L)) A B
(INFERS1 : Gamma ⊢ B)
: Gamma ⊢ Dis_frm A B.