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4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| The HELM team. *)
8 (* ||A|| http://helm.cs.unibo.it *)
10 (* \ / This file is distributed under the terms of the *)
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15 include "basics/logic.ma".
16 include "ground_2/xoa_notation.ma".
17 include "ground_2/xoa.ma".
19 interpretation "logical false" 'false = False.
21 interpretation "logical true" 'true = True.
23 lemma ex2_1_comm: ∀A0. ∀P0,P1:A0→Prop. (∃∃x0. P0 x0 & P1 x0) → ∃∃x0. P1 x0 & P0 x0.
24 #A0 #P0 #P1 * /2 width=3/