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14
15 include "basics/bool.ma".
16 include "ground_2/notation/constructors/no_0.ma".
17 include "ground_2/notation/constructors/yes_0.ma".
18
19 (* BOOLEAN PROPERTIES *******************************************************)
20
21 interpretation "boolean false" 'no = false.
22
23 interpretation "boolean true" 'yes = true.
24
25 lemma orb_false_r: ∀b1,b2:bool. (b1 ∨ b2) = false → b1 = false ∧ b2 = false.
26 * normalize /2 width=1 by conj/ #b2 #H destruct
27 qed-.
28
29 lemma commutative_orb: commutative … orb.
30 * * // qed.