lemma ylt_inv_Y2: ∀x. x < ∞ → ∃m. x = yinj m.
/2 width=3 by ylt_inv_Y2_aux/ 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 → ∃∃n. m < n & y = ⫯n.
+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
- @(ex2_intro … m) /2 width=1 by ylt_inj/ (**) (* explicit constructor *)
+ #m #Hnm #H destruct /3 width=1 by ylt_inj, conj/
| #x #y #H elim (ysucc_inv_inj_sn … H) -H
- #m #H #_ destruct
- @(ex2_intro … (∞)) /2 width=1 by/ (**) (* explicit constructor *)
+ #m #H #_ destruct /2 width=1 by ylt_Y, conj/
]
qed-.
-lemma ylt_inv_succ1: ∀m,y. ⫯m < y → ∃∃n. m < n & y = ⫯n.
+lemma ylt_inv_succ1: ∀m,y. ⫯m < y → m < ⫰y ∧ y = ⫯⫰y.
/2 width=3 by ylt_inv_succ1_aux/ qed-.
-lemma yle_inv_succ: ∀m,n. ⫯m < ⫯n → m < n.
-#m #n #H elim (ylt_inv_succ1 … H) -H
-#x #Hx #H destruct //
+lemma ylt_inv_succ: ∀m,n. ⫯m < ⫯n → m < n.
+#m #n #H elim (ylt_inv_succ1 … H) -H //
qed-.
-fact ylt_inv_succ2_aux: ∀x,y. x < y → ∀n. y = ⫯n → x ≤ n.
+(* 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/
]
qed-.
-lemma ylt_inv_succ2: ∀m,n. m < ⫯n → m ≤ n.
-/2 width=3 by ylt_inv_succ2_aux/ 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 **************************************)
]
qed-.
+(* Properties on successor **************************************************)
+
+lemma ylt_O_succ: ∀n. 0 < ⫯n.
+* /2 width=1 by ylt_inj/
+qed.
+
(* Properties on yle ********************************************************)
lemma yle_to_ylt_or_eq: ∀m:ynat. ∀n:ynat. m ≤ n → m < n ∨ m = n.
/3 width=3 by transitive_lt, ylt_inj/ (**) (* full auto too slow *)
| #x #z #H elim (ylt_yle_false … H) //
]
-qed-.
+qed-.