+++ /dev/null
-(**************************************************************************)
-(* ___ *)
-(* ||M|| *)
-(* ||A|| A project by Andrea Asperti *)
-(* ||T|| *)
-(* ||I|| Developers: *)
-(* ||T|| The HELM team. *)
-(* ||A|| http://helm.cs.unibo.it *)
-(* \ / *)
-(* \ / This file is distributed under the terms of the *)
-(* v GNU General Public License Version 2 *)
-(* *)
-(**************************************************************************)
-
-include "basic_2/static/sh.ma".
-
-(* SORT DEGREE **************************************************************)
-
-(* sort degree specification *)
-record sd (h:sh): Type[0] ≝ {
- deg : relation nat; (* degree of the sort *)
- deg_total: ∀k. ∃l. deg k l; (* functional relation axioms *)
- deg_mono : ∀k,l1,l2. deg k l1 → deg k l2 → l1 = l2;
- deg_next : ∀k,l. deg k l → deg (next h k) (l - 1) (* compatibility condition *)
-}.
-
-(* Notable specifications ***************************************************)
-
-definition deg_O: relation nat ≝ λk,l. l = 0.
-
-definition sd_O: ∀h. sd h ≝ λh. mk_sd h deg_O ….
-// /2 width=1/ /2 width=2/ qed.
-
-inductive deg_SO (h:sh) (k:nat) (k0:nat): predicate nat ≝
-| deg_SO_pos : ∀l0. (next h)^l0 k0 = k → deg_SO h k k0 (l0 + 1)
-| deg_SO_zero: ((∃l0. (next h)^l0 k0 = k) → ⊥) → deg_SO h k k0 0
-.
-
-fact deg_SO_inv_pos_aux: ∀h,k,k0,l0. deg_SO h k k0 l0 → ∀l. l0 = l + 1 →
- (next h)^l k0 = k.
-#h #k #k0 #l0 * -l0
-[ #l0 #Hl0 #l #H
- lapply (injective_plus_l … H) -H #H destruct //
-| #_ #l0 <plus_n_Sm #H destruct
-]
-qed.
-
-lemma deg_SO_inv_pos: ∀h,k,k0,l0. deg_SO h k k0 (l0 + 1) → (next h)^l0 k0 = k.
-/2 width=3/ qed-.
-
-lemma deg_SO_refl: ∀h,k. deg_SO h k k 1.
-#h #k @(deg_SO_pos … 0 ?) //
-qed.
-
-lemma deg_SO_gt: ∀h,k1,k2. k1 < k2 → deg_SO h k1 k2 0.
-#h #k1 #k2 #HK12 @deg_SO_zero * #l elim l -l normalize
-[ #H destruct
- elim (lt_refl_false … HK12)
-| #l #_ #H
- lapply (next_lt h ((next h)^l k2)) >H -H #H
- lapply (transitive_lt … H HK12) -k1 #H1
- lapply (nexts_le h k2 l) #H2
- lapply (le_to_lt_to_lt … H2 H1) -h -l #H
- elim (lt_refl_false … H)
-qed.
-
-definition sd_SO: ∀h. nat → sd h ≝ λh,k. mk_sd h (deg_SO h k) ….
-[ #k0
- lapply (nexts_dec h k0 k) * [ * /3 width=2/ | /4 width=2/ ]
-| #K0 #l1 #l2 * [ #l01 ] #H1 * [1,3: #l02 ] #H2 //
- [ < H2 in H1; -H2 #H
- lapply (nexts_inj … H) -H #H destruct //
- | elim (H1 ?) /2 width=2/
- | elim (H2 ?) /2 width=2/
- ]
-| #k0 #l0 *
- [ #l #H destruct elim l -l normalize /2 width=1/
- | #H1 @deg_SO_zero * #l #H2 destruct
- @H1 -H1 @(ex_intro … (S l)) /2 width=1/ (**) (* explicit constructor *)
- ]
-]
-qed.
-
-let rec sd_l (h:sh) (k:nat) (l:nat) on l : sd h ≝
- match l with
- [ O ⇒ sd_O h
- | S l ⇒ match l with
- [ O ⇒ sd_SO h k
- | _ ⇒ sd_l h (next h k) l
- ]
- ].
-
-(* Basic properties *********************************************************)
-
-lemma deg_pred: ∀h,g,k,l. deg h g (next h k) (l + 1) → deg h g k (l + 2).
-#h #g #k #l #H1
-elim (deg_total h g k) #l0 #H0
-lapply (deg_next … H0) #H2
-lapply (deg_mono … H1 H2) -H1 -H2 #H
-<(associative_plus l 1 1) >H <plus_minus_m_m // /2 width=3 by transitive_le/
-qed.
-
-lemma sd_l_SS: ∀h,k,l. sd_l h k (l + 2) = sd_l h (next h k) (l + 1).
-#h #k #l <plus_n_Sm <plus_n_Sm //
-qed.
-
-lemma sd_l_correct: ∀h,l,k. deg h (sd_l h k l) k l.
-#h #l @(nat_ind_plus … l) -l // #l @(nat_ind_plus … l) -l // /3 width=1/
-qed.