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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 "basic_2/unwind/sstas.ma".
16 include "basic_2/reducibility/ysc.ma".
17 include "basic_2/computation/cprs.ma".
19 (* "BIG TREE" ORDER FOR CLOSURES ********************************************)
21 definition ygt: ∀h. sd h → bi_relation lenv term ≝
22 λh,g. bi_TC … (ysc h g).
24 interpretation "'big tree' order (closure)"
25 'BTGreaterThan h g L1 T1 L2 T2 = (ygt h g L1 T1 L2 T2).
27 (* Basic eliminators ********************************************************)
29 lemma ygt_ind: ∀h,g,L1,T1. ∀R:relation2 lenv term.
30 (∀L2,T2. h ⊢ ⦃L1, T1⦄ ≻[g] ⦃L2, T2⦄ → R L2 T2) →
31 (∀L,T,L2,T2. h ⊢ ⦃L1, T1⦄ >[g] ⦃L, T⦄ → h ⊢ ⦃L, T⦄ ≻[g] ⦃L2, T2⦄ → R L T → R L2 T2) →
32 ∀L2,T2. h ⊢ ⦃L1, T1⦄ >[g] ⦃L2, T2⦄ → R L2 T2.
33 #h #g #L1 #T1 #R #IH1 #IH2 #L2 #T2 #H
34 @(bi_TC_ind … IH1 IH2 L2 T2 H)
35 qed-. (**) (* /3 width=6 by bi_TC_ind/ fails *)
37 lemma ygt_ind_dx: ∀h,g,L2,T2. ∀R:relation2 lenv term.
38 (∀L1,T1. h ⊢ ⦃L1, T1⦄ ≻[g] ⦃L2, T2⦄ → R L1 T1) →
39 (∀L1,L,T1,T. h ⊢ ⦃L1, T1⦄ ≻[g] ⦃L, T⦄ → h ⊢ ⦃L, T⦄ >[g] ⦃L2, T2⦄ → R L T → R L1 T1) →
40 ∀L1,T1. h ⊢ ⦃L1, T1⦄ >[g] ⦃L2, T2⦄ → R L1 T1.
41 /3 width=6 by bi_TC_ind_dx/ qed-.
43 (* Basic properties *********************************************************)
45 lemma ygt_strap1: ∀h,g,L1,L,L2,T1,T,T2. h ⊢ ⦃L1, T1⦄ >[g] ⦃L, T⦄ →
46 h ⊢ ⦃L, T⦄ ≻[g] ⦃L2, T2⦄ → h ⊢ ⦃L1, T1⦄ >[g] ⦃L2, T2⦄.
49 lemma ygt_strap2: ∀h,g,L1,L,L2,T1,T,T2. h ⊢ ⦃L1, T1⦄ ≻[g] ⦃L, T⦄ →
50 h ⊢ ⦃L, T⦄ >[g] ⦃L2, T2⦄ → h ⊢ ⦃L1, T1⦄ >[g] ⦃L2, T2⦄.
53 lemma ygt_cprs_trans: ∀h,g,L1,L,T1,T. h ⊢ ⦃L1, T1⦄ >[g] ⦃L, T⦄ →
54 ∀T2. L ⊢ T ➡* T2 → h ⊢ ⦃L1, T1⦄ >[g] ⦃L, T2⦄.
55 #h #g #L1 #L #T1 #T #HLT1 #T2 #H @(cprs_ind … H) -T2 //
56 #T0 #T2 #_ #HT02 #IHT0 -HLT1
57 elim (term_eq_dec T0 T2) #HT02 destruct //
58 @(ygt_strap1 … IHT0) /3 width=1/
61 lemma ygt_sstas_trans: ∀h,g,L1,L,T1,T. h ⊢ ⦃L1, T1⦄ >[g] ⦃L, T⦄ →
62 ∀T2. ⦃h, L⦄ ⊢ T •*[g] T2 → h ⊢ ⦃L1, T1⦄ >[g] ⦃L, T2⦄.
63 #h #g #L1 #L #T1 #T #HLT1 #T2 #H @(sstas_ind … H) -T2 //
64 #T0 #T2 #l #_ #HT02 #IHT0 -HLT1
65 @(ygt_strap1 … IHT0) -IHT0 /2 width=2/
68 lemma cprs_ygt_trans: ∀h,g,L,T1,T. L ⊢ T1 ➡* T →
69 ∀L2,T2. h ⊢ ⦃L, T⦄ >[g] ⦃L2, T2⦄ → h ⊢ ⦃L, T1⦄ >[g] ⦃L2, T2⦄.
70 #h #g #L #T1 #T #H @(cprs_ind … H) -T //
71 #T0 #T #_ #HT0 #IHT10 #L2 #T2 #HLT2
72 elim (term_eq_dec T0 T) #HT0 destruct /2 width=1/
73 @IHT10 -IHT10 @(ygt_strap2 … HLT2) /3 width=1/
76 lemma sstas_ygt_trans: ∀h,g,L,T1,T. ⦃h, L⦄ ⊢ T1 •*[g] T →
77 ∀L2,T2. h ⊢ ⦃L, T⦄ >[g] ⦃L2, T2⦄ → h ⊢ ⦃L, T1⦄ >[g] ⦃L2, T2⦄.
78 #h #g #L #T1 #T #H @(sstas_ind … H) -T //
79 #T0 #T #l #_ #HT0 #IHT10 #L2 #T2 #HLT2
80 @IHT10 -IHT10 @(ygt_strap2 … HLT2) /2 width=2/
83 lemma fw_ygt: ∀h,g,L1,L2,T1,T2. ♯{L2, T2} < ♯{L1, T1} → h ⊢ ⦃L1, T1⦄ >[g] ⦃L2, T2⦄.
86 lemma cprs_ygt: ∀h,g,L,T1,T2. L ⊢ T1 ➡* T2 → (T1 = T2 → ⊥) → h ⊢ ⦃L, T1⦄ >[g] ⦃L, T2⦄.
87 #h #g #L #T1 #T2 #H @(cprs_ind … H) -T2
89 | #T #T2 #_ #HT2 #IHT1 #H
90 elim (term_eq_dec T1 T) #HT1 destruct
91 [ -IHT1 /4 width=1 by ysc_cpr, bi_inj/ (**) (* auto too slow without trace *)
92 | -H /4 width=3 by inj, ygt_cprs_trans/