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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 *)
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11 (* v GNU General Public License Version 2 *)
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15 include "basic_2/syntax/term.ma".
17 (* BINDERS FOR LOCAL ENVIRONMENTS ******************************************)
19 inductive bind: Type[0] ≝
21 | BPair: bind2 → term → bind
24 inductive ext2 (R:relation term): relation bind ≝
25 | ext2_unit: ∀I. ext2 R (BUnit I) (BUnit I)
26 | ext2_pair: ∀I,V1,V2. R V1 V2 → ext2 R (BPair I V1) (BPair I V2)
29 (* Basic_inversion lemmas **************************************************)
31 fact ext2_inv_unit_sn_aux: ∀R,Z1,Z2. ext2 R Z1 Z2 →
32 ∀I. Z1 = BUnit I → Z2 = BUnit I.
33 #R #Z1 #Z2 * -Z1 -Z2 #I [2: #V1 #V2 #_ ]
37 lemma ext2_inv_unit_sn: ∀R,I,Z2. ext2 R (BUnit I) Z2 → Z2 = BUnit I.
38 /2 width=4 by ext2_inv_unit_sn_aux/ qed-.
40 fact ext2_inv_pair_sn_aux: ∀R,Z1,Z2. ext2 R Z1 Z2 →
41 ∀I,V1. Z1 = BPair I V1 →
42 ∃∃V2. R V1 V2 & Z2 = BPair I V2.
43 #R #Z1 #Z2 * -Z1 -Z2 #I [2: #V1 #V2 #HV12 ]
44 #J #W1 #H destruct /2 width=3 by ex2_intro/
47 lemma ext2_inv_pair_sn: ∀R,Z2,I,V1. ext2 R (BPair I V1) Z2 →
48 ∃∃V2. R V1 V2 & Z2 = BPair I V2.
49 /2 width=3 by ext2_inv_pair_sn_aux/ qed-.
51 fact ext2_inv_unit_dx_aux: ∀R,Z1,Z2. ext2 R Z1 Z2 →
52 ∀I. Z2 = BUnit I → Z1 = BUnit I.
53 #R #Z1 #Z2 * -Z1 -Z2 #I [2: #V1 #V2 #_ ]
57 lemma ext2_inv_unit_dx: ∀R,I,Z1. ext2 R Z1 (BUnit I) → Z1 = BUnit I.
58 /2 width=4 by ext2_inv_unit_dx_aux/ qed-.
60 fact ext2_inv_pair_dx_aux: ∀R,Z1,Z2. ext2 R Z1 Z2 →
61 ∀I,V2. Z2 = BPair I V2 →
62 ∃∃V1. R V1 V2 & Z1 = BPair I V1.
63 #R #Z1 #Z2 * -Z1 -Z2 #I [2: #V1 #V2 #HV12 ]
64 #J #W2 #H destruct /2 width=3 by ex2_intro/
67 lemma ext2_inv_pair_dx: ∀R,Z1,I,V2. ext2 R Z1 (BPair I V2) →
68 ∃∃V1. R V1 V2 & Z1 = BPair I V1.
69 /2 width=3 by ext2_inv_pair_dx_aux/ qed-.
71 (* Basic properties ********************************************************)
73 lemma eq_bind_dec: ∀I1,I2:bind. Decidable (I1 = I2).
74 * #I1 [2: #V1 ] * #I2 [2,4: #V2 ]
75 [1: elim (eq_bind2_dec I1 I2) #HI
76 [ elim (eq_term_dec V1 V2) #HV ]
77 |4: elim (eq_bind1_dec I1 I2) #HI
79 /2 width=1 by or_introl/
80 @or_intror #H destruct /2 width=1 by/
83 lemma ext2_refl: ∀R. reflexive … R → reflexive … (ext2 R).
84 #R #HR * /2 width=1 by ext2_pair/
87 lemma ext2_sym: ∀R. symmetric … R → symmetric … (ext2 R).
88 #R #HR #T1 #T2 * /3 width=1 by ext2_unit, ext2_pair/