matita/matita/contribs/lambdadelta/static_2/syntax/sh_lt.ma

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   2 (*       ___                                                              *)
   3 (*      ||M||                                                             *)
   4 (*      ||A||       A project by Andrea Asperti                           *)
   5 (*      ||T||                                                             *)
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  10 (*       \ /        This file is distributed under the terms of the       *)
  11 (*        v         GNU General Public License Version 2                  *)
  12 (*                                                                        *)
  13 (**************************************************************************)
  14
  15 include "ground/arith/nat_lt_minus.ma".
  16 include "static_2/syntax/sh_props.ma".
  17
  18 (* SORT HIERARCHY ***********************************************************)
  19
  20 (* strict monotonicity condition *)
  21 record sh_lt (h): Prop ≝
  22 {
  23   sh_next_lt: ∀s. s < ⇡[h]s
  24 }.
  25
  26 (* Basic properties *********************************************************)
  27
  28 lemma sh_nexts_le (h): sh_lt h → ∀s,n. s ≤ ⇡*[h,n]s.
  29 #h #Hh #s #n @(nat_ind_succ … n) -n [ // ] #n #IH <sh_nexts_succ
  30 lapply (sh_next_lt … Hh (⇡*[h,n]s)) #H
  31 lapply (nle_nlt_trans … IH H) -IH -H /2 width=2 by nlt_des_le/
  32 qed.
  33
  34 lemma sh_nexts_lt (h): sh_lt h → ∀s,n. s < ⇡*[h,↑n]s.
  35 #h #Hh #s #n <sh_nexts_succ
  36 lapply (sh_nexts_le … Hh s n) #H
  37 @(nle_nlt_trans … H) /2 width=1 by sh_next_lt/
  38 qed.
  39
  40 lemma sh_lt_nexts_inv_lt (h): sh_lt h →
  41       ∀s,n1,n2. ⇡*[h,n1]s < ⇡*[h,n2]s → n1 < n2.
  42 #h #Hh
  43 @pull_2 #n1
  44 @(nat_ind_succ … n1) -n1
  45 [ #s #n2 @(nat_ind_succ … n2) -n2
  46   [ #H elim (nlt_inv_refl … H)
  47   | #n2 #_ //
  48   ]
  49 | #n1 #IH #s #n2 @(nat_ind_succ … n2) -n2
  50   [ <sh_nexts_zero #H
  51     elim (nlt_inv_refl s)
  52     /3 width=3 by sh_nexts_lt, nlt_trans/
  53   | #n2 #_ <sh_nexts_succ_next <sh_nexts_succ_next #H
  54     /3 width=2 by nlt_succ_bi/
  55   ]
  56 ]
  57 qed-.
  58
  59 lemma sh_lt_acyclic (h): sh_lt h → sh_acyclic h.
  60 #h #Hh
  61 @mk_sh_acyclic
  62 @pull_2 #n1
  63 @(nat_ind_succ … n1) -n1
  64 [ #s #n2 @(nat_ind_succ … n2) -n2 [ // ] #n2 #_ <sh_nexts_zero #H
  65   elim (nlt_inv_refl s) >H in ⊢ (??%); -H
  66   /2 width=1 by sh_nexts_lt/
  67 | #n1 #IH #s #n2 @(nat_ind_succ … n2) -n2
  68   [ <sh_nexts_zero #H -IH
  69     elim (nlt_inv_refl s) <H in ⊢ (??%); -H
  70     /2 width=1 by sh_nexts_lt/
  71   | #n2 #_ <sh_nexts_succ_next <sh_nexts_succ_next #H
  72     lapply (IH … H) -IH -H //
  73   ]
  74 ]
  75 qed.
  76
  77 lemma sh_lt_dec (h): sh_lt h → sh_decidable h.
  78 #h #Hh
  79 @mk_sh_decidable #s1 #s2
  80 elim (nat_split_lt_ge s2 s1) #Hs
  81 [ @or_intror * #n #H destruct
  82   @(nlt_ge_false … Hs) /2 width=1 by sh_nexts_le/ (**) (* full auto too slow *)
  83 | @(nle_ind_sn … Hs) -s1 -s2 #s1 #s2 #IH #Hs12
  84   elim (nat_split_lt_eq_gt s2 (⇡[h]s1)) #Hs21 destruct
  85   [ elim (nle_split_lt_eq … Hs12) -Hs12 #Hs12 destruct
  86     [ -IH @or_intror * #n #H destruct
  87       generalize in match Hs21; -Hs21
  88       >sh_nexts_unit #H
  89       lapply (sh_lt_nexts_inv_lt … Hh … H) -H #H
  90       <(nle_inv_zero_dx n) in Hs12;
  91       /2 width=2 by nlt_inv_refl, nle_inv_succ_bi/
  92     | /3 width=2 by ex_intro, or_introl/
  93     ]
  94   | -IH @or_introl @(ex_intro … 𝟏) // (**) (* auto fails *)
  95   | lapply (nlt_trans s1 ??? Hs21) [ /2 width=1 by sh_next_lt/ ] -Hs12 #Hs12
  96     elim (IH (s2-⇡[h]s1)) -IH
  97     [3: /3 width=1 by sh_next_lt, nlt_minus_bi_sn/ ]
  98     <nminus_minus_dx_refl_sn [2,4: /2 width=1 by nlt_des_le/ ] -Hs21
  99     [ * #n #H destruct
 100       @or_introl @(ex_intro … (↑n)) //
 101     | #H1 @or_intror * #n #H2 @H1 -H1 destruct
 102       generalize in match Hs12; -Hs12
 103       >(sh_nexts_zero h s1) in ⊢ (?%?→?); #H
 104       lapply (sh_lt_nexts_inv_lt … Hh … H) -H #H
 105       >(nlt_des_gen … H) -H
 106       @(ex_intro … (↓n)) //
 107     ]
 108   ]
 109 ]
 110 qed-.