+++ /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 "ground_2A/ynat/ynat_le.ma".
-
-(* NATURAL NUMBERS WITH INFINITY ********************************************)
-
-(* strict order relation *)
-inductive ylt: relation ynat ≝
-| ylt_inj: ∀m,n. m < n → ylt m n
-| ylt_Y : ∀m:nat. ylt m (∞)
-.
-
-interpretation "ynat 'less than'" 'lt x y = (ylt x y).
-
-(* Basic forward lemmas *****************************************************)
-
-lemma ylt_fwd_gen: ∀x,y. x < y → ∃m. x = yinj m.
-#x #y * -x -y /2 width=2 by ex_intro/
-qed-.
-
-lemma ylt_fwd_le_succ: ∀x,y. x < y → ⫯x ≤ y.
-#x #y * -x -y /2 width=1 by yle_inj/
-qed-.
-
-(* Basic inversion lemmas ***************************************************)
-
-fact ylt_inv_inj2_aux: ∀x,y. x < y → ∀n. y = yinj n →
- ∃∃m. m < n & x = yinj m.
-#x #y * -x -y
-[ #x #y #Hxy #n #Hy elim (le_inv_S1 … Hxy) -Hxy
- #m #Hm #H destruct /3 width=3 by le_S_S, ex2_intro/
-| #x #n #Hy destruct
-]
-qed-.
-
-lemma ylt_inv_inj2: ∀x,n. x < yinj n →
- ∃∃m. m < n & x = yinj m.
-/2 width=3 by ylt_inv_inj2_aux/ qed-.
-
-lemma ylt_inv_inj: ∀m,n. yinj m < yinj n → m < n.
-#m #n #H elim (ylt_inv_inj2 … H) -H
-#x #Hx #H destruct //
-qed-.
-
-lemma ylt_inv_Y1: ∀n. ∞ < n → ⊥.
-#n #H elim (ylt_fwd_gen … H) -H
-#y #H destruct
-qed-.
-
-lemma ylt_inv_O1: ∀n. 0 < n → ⫯⫰n = n.
-* // #n #H lapply (ylt_inv_inj … H) -H normalize
-/3 width=1 by S_pred, eq_f/
-qed-.
-
-(* Inversion lemmas on successor ********************************************)
-
-fact ylt_inv_succ1_aux: ∀x,y. x < y → ∀m. x = ⫯m → m < ⫰y ∧ ⫯⫰y = y.
-#x #y * -x -y
-[ #x #y #Hxy #m #H elim (ysucc_inv_inj_sn … H) -H
- #n #H1 #H2 destruct elim (le_inv_S1 … Hxy) -Hxy
- #m #Hnm #H destruct /3 width=1 by ylt_inj, conj/
-| #x #y #H elim (ysucc_inv_inj_sn … H) -H
- #m #H #_ destruct /2 width=1 by ylt_Y, conj/
-]
-qed-.
-
-lemma ylt_inv_succ1: ∀m,y. ⫯m < y → m < ⫰y ∧ ⫯⫰y = y.
-/2 width=3 by ylt_inv_succ1_aux/ qed-.
-
-lemma ylt_inv_succ: ∀m,n. ⫯m < ⫯n → m < n.
-#m #n #H elim (ylt_inv_succ1 … H) -H //
-qed-.
-
-(* Forward lemmas on successor **********************************************)
-
-fact ylt_fwd_succ2_aux: ∀x,y. x < y → ∀n. y = ⫯n → x ≤ n.
-#x #y * -x -y
-[ #x #y #Hxy #m #H elim (ysucc_inv_inj_sn … H) -H
- #n #H1 #H2 destruct /3 width=1 by yle_inj, le_S_S_to_le/
-| #x #n #H lapply (ysucc_inv_Y_sn … H) -H //
-]
-qed-.
-
-lemma ylt_fwd_succ2: ∀m,n. m < ⫯n → m ≤ n.
-/2 width=3 by ylt_fwd_succ2_aux/ qed-.
-
-(* inversion and forward lemmas on yle **************************************)
-
-lemma ylt_fwd_le_succ1: ∀m,n. m < n → ⫯m ≤ n.
-#m #n * -m -n /2 width=1 by yle_inj/
-qed-.
-
-lemma ylt_fwd_le: ∀m:ynat. ∀n:ynat. m < n → m ≤ n.
-#m #n * -m -n /3 width=1 by lt_to_le, yle_inj/
-qed-.
-
-lemma ylt_yle_false: ∀m:ynat. ∀n:ynat. m < n → n ≤ m → ⊥.
-#m #n * -m -n
-[ #m #n #Hmn #H lapply (yle_inv_inj … H) -H
- #H elim (lt_refl_false n) /2 width=3 by le_to_lt_to_lt/
-| #m #H lapply (yle_inv_Y1 … H) -H
- #H destruct
-]
-qed-.
-
-(* Basic properties *********************************************************)
-
-lemma ylt_O: ∀x. ⫯⫰(yinj x) = yinj x → 0 < x.
-* /2 width=1 by/ normalize
-#H destruct
-qed.
-
-(* Properties on predecessor ************************************************)
-
-lemma ylt_pred: ∀m,n. m < n → 0 < m → ⫰m < ⫰n.
-#m #n * -m -n
-/4 width=1 by ylt_inv_inj, ylt_inj, monotonic_lt_pred/
-qed.
-
-(* Properties on successor **************************************************)
-
-lemma ylt_O_succ: ∀n. 0 < ⫯n.
-* /2 width=1 by ylt_inj/
-qed.
-
-lemma ylt_succ: ∀m,n. m < n → ⫯m < ⫯n.
-#m #n #H elim H -m -n /3 width=1 by ylt_inj, le_S_S/
-qed.
-
-(* Properties on order ******************************************************)
-
-lemma yle_split_eq: ∀m:ynat. ∀n:ynat. m ≤ n → m < n ∨ m = n.
-#m #n * -m -n
-[ #m #n #Hmn elim (le_to_or_lt_eq … Hmn) -Hmn
- /3 width=1 by or_introl, ylt_inj/
-| * /2 width=1 by or_introl, ylt_Y/
-]
-qed-.
-
-lemma ylt_split: ∀m,n:ynat. m < n ∨ n ≤ m..
-#m #n elim (yle_split m n) /2 width=1 by or_intror/
-#H elim (yle_split_eq … H) -H /2 width=1 by or_introl, or_intror/
-qed-.
-
-lemma ylt_yle_trans: ∀x:ynat. ∀y:ynat. ∀z:ynat. y ≤ z → x < y → x < z.
-#x #y #z * -y -z
-[ #y #z #Hyz #H elim (ylt_inv_inj2 … H) -H
- #m #Hm #H destruct /3 width=3 by ylt_inj, lt_to_le_to_lt/
-| #y * //
-]
-qed-.
-
-lemma yle_ylt_trans: ∀x:ynat. ∀y:ynat. ∀z:ynat. y < z → x ≤ y → x < z.
-#x #y #z * -y -z
-[ #y #z #Hyz #H elim (yle_inv_inj2 … H) -H
- #m #Hm #H destruct /3 width=3 by ylt_inj, le_to_lt_to_lt/
-| #y #H elim (yle_inv_inj2 … H) -H //
-]
-qed-.
-
-(* Main properties **********************************************************)
-
-theorem ylt_trans: Transitive … ylt.
-#x #y * -x -y
-[ #x #y #Hxy * //
- #z #H lapply (ylt_inv_inj … H) -H
- /3 width=3 by transitive_lt, ylt_inj/ (**) (* full auto too slow *)
-| #x #z #H elim (ylt_yle_false … H) //
-]
-qed-.
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