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4 (* ||A|| A project by Andrea Asperti *)
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15 include "Ground_2/xoa_notation.ma".
16 include "Ground_2/xoa.ma".
18 lemma ex2_1_comm: ∀A0. ∀P0,P1:A0→Prop. (∃∃x0. P0 x0 & P1 x0) → ∃∃x0. P1 x0 & P0 x0.
19 #A0 #P0 #P1 * /2 width=3/