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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 lemma TC_strip1: ∀A,R1,R2. confluent2 A R1 R2 →
39 ∀a0,a1. TC … R1 a0 a1 → ∀a2. R2 a0 a2 →
40 ∃∃a. R2 a1 a & TC … R1 a2 a.
41 #A #R1 #R2 #HR12 #a0 #a1 #H elim H -a1
43 elim (HR12 … Ha01 … Ha02) -HR12 -a0 /3 width=3/
44 | #a #a1 #_ #Ha1 #IHa0 #a2 #Ha02
45 elim (IHa0 … Ha02) -a0 #a0 #Ha0 #Ha20
46 elim (HR12 … Ha1 … Ha0) -HR12 -a /4 width=3/
50 lemma TC_strip2: ∀A,R1,R2. confluent2 A R1 R2 →
51 ∀a0,a2. TC … R2 a0 a2 → ∀a1. R1 a0 a1 →
52 ∃∃a. TC … R2 a1 a & R1 a2 a.
53 #A #R1 #R2 #HR12 #a0 #a2 #H elim H -a2
55 elim (HR12 … Ha01 … Ha02) -HR12 -a0 /3 width=3/
56 | #a #a2 #_ #Ha2 #IHa0 #a1 #Ha01
57 elim (IHa0 … Ha01) -a0 #a0 #Ha10 #Ha0
58 elim (HR12 … Ha0 … Ha2) -HR12 -a /4 width=3/
62 lemma TC_confluent2: ∀A,R1,R2.
63 confluent2 A R1 R2 → confluent2 A (TC … R1) (TC … R2).
64 #A #R1 #R2 #HR12 #a0 #a1 #H elim H -a1
66 elim (TC_strip2 … HR12 … Ha02 … Ha01) -HR12 -a0 /3 width=3/
67 | #a #a1 #_ #Ha1 #IHa0 #a2 #Ha02
68 elim (IHa0 … Ha02) -a0 #a0 #Ha0 #Ha20
69 elim (TC_strip2 … HR12 … Ha0 … Ha1) -HR12 -a /4 width=3/
73 lemma TC_strap1: ∀A,R1,R2. transitive2 A R1 R2 →
74 ∀a1,a0. TC … R1 a1 a0 → ∀a2. R2 a0 a2 →
75 ∃∃a. R2 a1 a & TC … R1 a a2.
76 #A #R1 #R2 #HR12 #a1 #a0 #H elim H -a0
78 elim (HR12 … Ha10 … Ha02) -HR12 -a0 /3 width=3/
79 | #a #a0 #_ #Ha0 #IHa #a2 #Ha02
80 elim (HR12 … Ha0 … Ha02) -HR12 -a0 #a0 #Ha0 #Ha02
81 elim (IHa … Ha0) -a /4 width=3/
85 lemma TC_strap2: ∀A,R1,R2. transitive2 A R1 R2 →
86 ∀a0,a2. TC … R2 a0 a2 → ∀a1. R1 a1 a0 →
87 ∃∃a. TC … R2 a1 a & R1 a a2.
88 #A #R1 #R2 #HR12 #a0 #a2 #H elim H -a2
90 elim (HR12 … Ha10 … Ha02) -HR12 -a0 /3 width=3/
91 | #a #a2 #_ #Ha02 #IHa #a1 #Ha10
92 elim (IHa … Ha10) -a0 #a0 #Ha10 #Ha0
93 elim (HR12 … Ha0 … Ha02) -HR12 -a /4 width=3/
97 lemma TC_transitive2: ∀A,R1,R2.
98 transitive2 A R1 R2 → transitive2 A (TC … R1) (TC … R2).
99 #A #R1 #R2 #HR12 #a1 #a0 #H elim H -a0
100 [ #a0 #Ha10 #a2 #Ha02
101 elim (TC_strap2 … HR12 … Ha02 … Ha10) -HR12 -a0 /3 width=3/
102 | #a #a0 #_ #Ha0 #IHa #a2 #Ha02
103 elim (TC_strap2 … HR12 … Ha02 … Ha0) -HR12 -a0 #a0 #Ha0 #Ha02
104 elim (IHa … Ha0) -a /4 width=3/
108 definition NF: ∀A. relation A → relation A → predicate A ≝
109 λA,R,S,a1. ∀a2. R a1 a2 → S a2 a1.
111 inductive SN (A) (R,S:relation A): predicate A ≝
112 | SN_intro: ∀a1. (∀a2. R a1 a2 → (S a2 a1 → ⊥) → SN A R S a2) → SN A R S a1
115 lemma NF_to_SN: ∀A,R,S,a. NF A R S a → SN A R S a.
117 @SN_intro #a2 #HRa12 #HSa12
118 elim (HSa12 ?) -HSa12 /2 width=1/
121 definition NF_sn: ∀A. relation A → relation A → predicate A ≝
122 λA,R,S,a2. ∀a1. R a1 a2 → S a2 a1.
124 inductive SN_sn (A) (R,S:relation A): predicate A ≝
125 | SN_sn_intro: ∀a2. (∀a1. R a1 a2 → (S a2 a1 → ⊥) → SN_sn A R S a1) → SN_sn A R S a2
128 lemma NF_to_SN_sn: ∀A,R,S,a. NF_sn A R S a → SN_sn A R S a.
130 @SN_sn_intro #a1 #HRa12 #HSa12
131 elim (HSa12 ?) -HSa12 /2 width=1/