1 (**************************************************************************)
4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| The HELM team. *)
8 (* ||A|| http://helm.cs.unibo.it *)
10 (* \ / This file is distributed under the terms of the *)
11 (* v GNU General Public License Version 2 *)
13 (**************************************************************************)
15 include "ground_2/ynat/ynat_le.ma".
17 (* NATURAL NUMBERS WITH INFINITY ********************************************)
19 (* strict order relation *)
20 inductive ylt: relation ynat ≝
21 | ylt_inj: ∀m,n. m < n → ylt m n
22 | ylt_Y : ∀m:nat. ylt m (∞)
25 interpretation "ynat 'less than'" 'lt x y = (ylt x y).
27 (* Basic forward lemmas *****************************************************)
29 lemma ylt_inv_gen: ∀x,y. x < y → ∃m. x = yinj m.
30 #x #y * -x -y /2 width=2 by ex_intro/
33 (* Basic inversion lemmas ***************************************************)
35 fact ylt_inv_inj2_aux: ∀x,y. x < y → ∀n. y = yinj n →
36 ∃∃m. m < n & x = yinj m.
38 [ #x #y #Hxy #n #Hy elim (le_inv_S1 … Hxy) -Hxy
39 #m #Hm #H destruct /3 width=3 by le_S_S, ex2_intro/
44 lemma ylt_inv_inj2: ∀x,n. x < yinj n →
45 ∃∃m. m < n & x = yinj m.
46 /2 width=3 by ylt_inv_inj2_aux/ qed-.
48 lemma ylt_inv_inj: ∀m,n. yinj m < yinj n → m < n.
49 #m #n #H elim (ylt_inv_inj2 … H) -H
53 lemma ylt_inv_Y1: ∀n. ∞ < n → ⊥.
54 #n #H elim (ylt_inv_gen … H) -H
58 lemma ylt_inv_O1: ∀n. 0 < n → ⫯⫰n = n.
59 * // #n #H lapply (ylt_inv_inj … H) -H normalize
60 /3 width=1 by S_pred, eq_f/
63 (* Inversion lemmas on successor ********************************************)
65 fact ylt_inv_succ1_aux: ∀x,y. x < y → ∀m. x = ⫯m → m < ⫰y ∧ ⫯⫰y = y.
67 [ #x #y #Hxy #m #H elim (ysucc_inv_inj_sn … H) -H
68 #n #H1 #H2 destruct elim (le_inv_S1 … Hxy) -Hxy
69 #m #Hnm #H destruct /3 width=1 by ylt_inj, conj/
70 | #x #y #H elim (ysucc_inv_inj_sn … H) -H
71 #m #H #_ destruct /2 width=1 by ylt_Y, conj/
75 lemma ylt_inv_succ1: ∀m,y. ⫯m < y → m < ⫰y ∧ ⫯⫰y = y.
76 /2 width=3 by ylt_inv_succ1_aux/ qed-.
78 lemma ylt_inv_succ: ∀m,n. ⫯m < ⫯n → m < n.
79 #m #n #H elim (ylt_inv_succ1 … H) -H //
82 (* Forward lemmas on successor **********************************************)
84 fact ylt_fwd_succ2_aux: ∀x,y. x < y → ∀n. y = ⫯n → x ≤ n.
86 [ #x #y #Hxy #m #H elim (ysucc_inv_inj_sn … H) -H
87 #n #H1 #H2 destruct /3 width=1 by yle_inj, le_S_S_to_le/
88 | #x #n #H lapply (ysucc_inv_Y_sn … H) -H //
92 lemma ylt_fwd_succ2: ∀m,n. m < ⫯n → m ≤ n.
93 /2 width=3 by ylt_fwd_succ2_aux/ qed-.
95 (* inversion and forward lemmas on yle **************************************)
97 lemma lt_fwd_le: ∀m:ynat. ∀n:ynat. m < n → m ≤ n.
98 #m #n * -m -n /3 width=1 by yle_pred_sn, yle_inj, yle_Y/
101 lemma ylt_yle_false: ∀m:ynat. ∀n:ynat. m < n → n ≤ m → ⊥.
103 [ #m #n #Hmn #H lapply (yle_inv_inj … H) -H
104 #H elim (lt_refl_false n) /2 width=3 by le_to_lt_to_lt/
105 | #m #H lapply (yle_inv_Y1 … H) -H
110 (* Basic properties *********************************************************)
112 lemma ylt_O: ∀x. ⫯⫰(yinj x) = yinj x → 0 < x.
113 * /2 width=1 by/ normalize
117 (* Properties on successor **************************************************)
119 lemma ylt_O_succ: ∀n. 0 < ⫯n.
120 * /2 width=1 by ylt_inj/
123 lemma ylt_succ: ∀m,n. m < n → ⫯m < ⫯n.
124 #m #n #H elim H -m -n /3 width=1 by ylt_inj, le_S_S/
127 (* Properties on order ******************************************************)
129 lemma yle_split_eq: ∀m:ynat. ∀n:ynat. m ≤ n → m < n ∨ m = n.
131 [ #m #n #Hmn elim (le_to_or_lt_eq … Hmn) -Hmn
132 /3 width=1 by or_introl, ylt_inj/
133 | * /2 width=1 by or_introl, ylt_Y/
137 lemma ylt_split: ∀m,n:ynat. m < n ∨ n ≤ m..
138 #m #n elim (yle_split m n) /2 width=1 by or_intror/
139 #H elim (yle_split_eq … H) -H /2 width=1 by or_introl, or_intror/
142 lemma ylt_yle_trans: ∀x:ynat. ∀y:ynat. ∀z:ynat. y ≤ z → x < y → x < z.
144 [ #y #z #Hyz #H elim (ylt_inv_inj2 … H) -H
145 #m #Hm #H destruct /3 width=3 by ylt_inj, lt_to_le_to_lt/
150 lemma yle_ylt_trans: ∀x:ynat. ∀y:ynat. ∀z:ynat. y < z → x ≤ y → x < z.
152 [ #y #z #Hyz #H elim (yle_inv_inj2 … H) -H
153 #m #Hm #H destruct /3 width=3 by ylt_inj, le_to_lt_to_lt/
154 | #y #H elim (yle_inv_inj2 … H) -H //
158 (* Main properties **********************************************************)
160 theorem ylt_trans: Transitive … ylt.
163 #z #H lapply (ylt_inv_inj … H) -H
164 /3 width=3 by transitive_lt, ylt_inj/ (**) (* full auto too slow *)
165 | #x #z #H elim (ylt_yle_false … H) //