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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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15 include "basics/star.ma".
16 include "ground_2/xoa_props.ma".
17 include "ground_2/notation.ma".
19 (* PROPERTIES OF RELATIONS **************************************************)
21 definition Decidable: Prop → Prop ≝ λR. R ∨ (R → ⊥).
23 definition Confluent: ∀A. ∀R: relation A. Prop ≝ λA,R.
24 ∀a0,a1. R a0 a1 → ∀a2. R a0 a2 →
27 definition Transitive: ∀A. ∀R: relation A. Prop ≝ λA,R.
28 ∀a1,a0. R a1 a0 → ∀a2. R a0 a2 → R a1 a2.
30 definition confluent2: ∀A. ∀R1,R2: relation A. Prop ≝ λA,R1,R2.
31 ∀a0,a1. R1 a0 a1 → ∀a2. R2 a0 a2 →
32 ∃∃a. R2 a1 a & R1 a2 a.
34 definition transitive2: ∀A. ∀R1,R2: relation A. Prop ≝ λA,R1,R2.
35 ∀a1,a0. R1 a1 a0 → ∀a2. R2 a0 a2 →
36 ∃∃a. R2 a1 a & R1 a a2.
38 definition bi_confluent: ∀A,B. ∀R: bi_relation A B. Prop ≝ λA,B,R.
39 ∀a0,a1,b0,b1. R a0 b0 a1 b1 → ∀a2,b2. R a0 b0 a2 b2 →
40 ∃∃a,b. R a1 b1 a b & R a2 b2 a b.
42 lemma TC_strip1: ∀A,R1,R2. confluent2 A R1 R2 →
43 ∀a0,a1. TC … R1 a0 a1 → ∀a2. R2 a0 a2 →
44 ∃∃a. R2 a1 a & TC … R1 a2 a.
45 #A #R1 #R2 #HR12 #a0 #a1 #H elim H -a1
47 elim (HR12 … Ha01 … Ha02) -HR12 -a0 /3 width=3/
48 | #a #a1 #_ #Ha1 #IHa0 #a2 #Ha02
49 elim (IHa0 … Ha02) -a0 #a0 #Ha0 #Ha20
50 elim (HR12 … Ha1 … Ha0) -HR12 -a /4 width=3/
54 lemma TC_strip2: ∀A,R1,R2. confluent2 A R1 R2 →
55 ∀a0,a2. TC … R2 a0 a2 → ∀a1. R1 a0 a1 →
56 ∃∃a. TC … R2 a1 a & R1 a2 a.
57 #A #R1 #R2 #HR12 #a0 #a2 #H elim H -a2
59 elim (HR12 … Ha01 … Ha02) -HR12 -a0 /3 width=3/
60 | #a #a2 #_ #Ha2 #IHa0 #a1 #Ha01
61 elim (IHa0 … Ha01) -a0 #a0 #Ha10 #Ha0
62 elim (HR12 … Ha0 … Ha2) -HR12 -a /4 width=3/
66 lemma TC_confluent2: ∀A,R1,R2.
67 confluent2 A R1 R2 → confluent2 A (TC … R1) (TC … R2).
68 #A #R1 #R2 #HR12 #a0 #a1 #H elim H -a1
70 elim (TC_strip2 … HR12 … Ha02 … Ha01) -HR12 -a0 /3 width=3/
71 | #a #a1 #_ #Ha1 #IHa0 #a2 #Ha02
72 elim (IHa0 … Ha02) -a0 #a0 #Ha0 #Ha20
73 elim (TC_strip2 … HR12 … Ha0 … Ha1) -HR12 -a /4 width=3/
77 lemma TC_strap1: ∀A,R1,R2. transitive2 A R1 R2 →
78 ∀a1,a0. TC … R1 a1 a0 → ∀a2. R2 a0 a2 →
79 ∃∃a. R2 a1 a & TC … R1 a a2.
80 #A #R1 #R2 #HR12 #a1 #a0 #H elim H -a0
82 elim (HR12 … Ha10 … Ha02) -HR12 -a0 /3 width=3/
83 | #a #a0 #_ #Ha0 #IHa #a2 #Ha02
84 elim (HR12 … Ha0 … Ha02) -HR12 -a0 #a0 #Ha0 #Ha02
85 elim (IHa … Ha0) -a /4 width=3/
89 lemma TC_strap2: ∀A,R1,R2. transitive2 A R1 R2 →
90 ∀a0,a2. TC … R2 a0 a2 → ∀a1. R1 a1 a0 →
91 ∃∃a. TC … R2 a1 a & R1 a a2.
92 #A #R1 #R2 #HR12 #a0 #a2 #H elim H -a2
94 elim (HR12 … Ha10 … Ha02) -HR12 -a0 /3 width=3/
95 | #a #a2 #_ #Ha02 #IHa #a1 #Ha10
96 elim (IHa … Ha10) -a0 #a0 #Ha10 #Ha0
97 elim (HR12 … Ha0 … Ha02) -HR12 -a /4 width=3/
101 lemma TC_transitive2: ∀A,R1,R2.
102 transitive2 A R1 R2 → transitive2 A (TC … R1) (TC … R2).
103 #A #R1 #R2 #HR12 #a1 #a0 #H elim H -a0
104 [ #a0 #Ha10 #a2 #Ha02
105 elim (TC_strap2 … HR12 … Ha02 … Ha10) -HR12 -a0 /3 width=3/
106 | #a #a0 #_ #Ha0 #IHa #a2 #Ha02
107 elim (TC_strap2 … HR12 … Ha02 … Ha0) -HR12 -a0 #a0 #Ha0 #Ha02
108 elim (IHa … Ha0) -a /4 width=3/
112 definition NF: ∀A. relation A → relation A → predicate A ≝
113 λA,R,S,a1. ∀a2. R a1 a2 → S a2 a1.
115 inductive SN (A) (R,S:relation A): predicate A ≝
116 | SN_intro: ∀a1. (∀a2. R a1 a2 → (S a2 a1 → ⊥) → SN A R S a2) → SN A R S a1
119 lemma NF_to_SN: ∀A,R,S,a. NF A R S a → SN A R S a.
121 @SN_intro #a2 #HRa12 #HSa12
122 elim (HSa12 ?) -HSa12 /2 width=1/
125 definition NF_sn: ∀A. relation A → relation A → predicate A ≝
126 λA,R,S,a2. ∀a1. R a1 a2 → S a2 a1.
128 inductive SN_sn (A) (R,S:relation A): predicate A ≝
129 | SN_sn_intro: ∀a2. (∀a1. R a1 a2 → (S a2 a1 → ⊥) → SN_sn A R S a1) → SN_sn A R S a2
132 lemma NF_to_SN_sn: ∀A,R,S,a. NF_sn A R S a → SN_sn A R S a.
134 @SN_sn_intro #a1 #HRa12 #HSa12
135 elim (HSa12 ?) -HSa12 /2 width=1/
138 lemma bi_TC_strip: ∀A,B,R. bi_confluent A B R →
139 ∀a0,a1,b0,b1. R a0 b0 a1 b1 → ∀a2,b2. bi_TC … R a0 b0 a2 b2 →
140 ∃∃a,b. bi_TC … R a1 b1 a b & R a2 b2 a b.
141 #A #B #R #HR #a0 #a1 #b0 #b1 #H01 #a2 #b2 #H elim H -a2 -b2
143 elim (HR … H01 … H02) -HR -a0 -b0 /3 width=4/
144 | #a2 #b2 #a3 #b3 #_ #H23 * #a #b #H1 #H2
145 elim (HR … H23 … H2) -HR -a0 -b0 -a2 -b2 /3 width=4/
149 lemma bi_TC_confluent: ∀A,B,R. bi_confluent A B R →
150 bi_confluent A B (bi_TC … R).
151 #A #B #R #HR #a0 #a1 #b0 #b1 #H elim H -a1 -b1
152 [ #a1 #b1 #H01 #a2 #b2 #H02
153 elim (bi_TC_strip … HR … H01 … H02) -a0 -b0 /3 width=4/
154 | #a1 #b1 #a3 #b3 #_ #H13 #IH #a2 #b2 #H02
155 elim (IH … H02) -a0 -b0 #a0 #b0 #H10 #H20
156 elim (bi_TC_strip … HR … H13 … H10) -a1 -b1 /3 width=7/