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4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| The HELM team. *)
8 (* ||A|| http://helm.cs.unibo.it *)
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15 include "ground/insert_eq/insert_eq_0.ma".
16 include "ground/arith/nat_succ.ma".
18 (* ORDER FOR NON-NEGATIVE INTEGERS ******************************************)
22 inductive nle (m:nat): predicate nat ≝
24 | nle_succ_dx: ∀n. nle m n → nle m (↑n)
28 "less equal (non-negative integers)"
31 (* Basic constructions ******************************************************)
34 lemma nle_succ_dx_refl (m): m ≤ ↑m.
35 /2 width=1 by nle_refl, nle_succ_dx/ qed.
38 lemma nle_zero_sx (m): 𝟎 ≤ m.
39 #m @(nat_ind … m) -m /2 width=1 by nle_succ_dx/
43 lemma nle_succ_bi (m) (n): m ≤ n → ↑m ≤ ↑n.
44 #m #n #H elim H -n /2 width=1 by nle_refl, nle_succ_dx/
48 lemma nle_ge_e (m) (n): ∨∨ m ≤ n | n ≤ m.
49 #m @(nat_ind … m) -m [ /2 width=1 by or_introl/ ]
50 #m #IH #n @(nat_ind … n) -n [ /2 width=1 by or_intror/ ]
51 #n #_ elim (IH n) -IH /3 width=2 by nle_succ_bi, or_introl, or_intror/
54 (* Basic inversions *********************************************************)
56 lemma nle_inv_succ_sn (m) (n): ↑m ≤ n → m ≤ n.
57 #m #n #H elim H -n /2 width=1 by nle_succ_dx/
61 lemma nle_inv_succ_bi (m) (n): ↑m ≤ ↑n → m ≤ n.
62 #m #n @(insert_eq_0 … (↑n))
64 [ #H <(eq_inv_nsucc_bi … H) -m //
65 | #y #Hy #H >(eq_inv_nsucc_bi … H) -n /2 width=1 by nle_inv_succ_sn/
70 lemma nle_inv_zero_dx (m): m ≤ 𝟎 → 𝟎 = m.
71 #m @(insert_eq_0 … (𝟎))
74 | #y #_ #H elim (eq_inv_nzero_succ … H)
78 (* Advanced inversions ******************************************************)
80 lemma nle_inv_succ_zero (m): ↑m ≤ 𝟎 → ⊥.
81 /3 width=2 by nle_inv_zero_dx, eq_inv_nzero_succ/ qed-.
83 lemma nle_inv_succ_sn_refl (m): ↑m ≤ m → ⊥.
84 #m @(nat_ind … m) -m [| #m #IH ] #H
85 [ /3 width=2 by nle_inv_zero_dx, eq_inv_nzero_succ/
86 | /3 width=1 by nle_inv_succ_bi/
90 (*** le_to_le_to_eq *)
91 theorem nle_antisym (m) (n): m ≤ n → n ≤ m → m = n.
94 lapply (nle_inv_succ_sn … Hn) #H
95 lapply (IH H) -IH -H #H destruct
96 elim (nle_inv_succ_sn_refl … Hn)
99 (* Advanced eliminations ****************************************************)
101 lemma nle_ind_alt (Q: relation2 nat nat):
103 (∀m,n. m ≤ n → Q m n → Q (↑m) (↑n)) →
105 #Q #IH1 #IH2 #m #n @(nat_ind_2 … m n) -m -n //
106 [ #m #H elim (nle_inv_succ_zero … H)
107 | /4 width=1 by nle_inv_succ_bi/
111 (* Advanced constructions ***************************************************)
113 (*** transitive_le *)
114 theorem nle_trans: Transitive … nle.
115 #m #n #H elim H -n /3 width=1 by nle_inv_succ_sn/
119 lemma nle_dec (m) (n): Decidable … (m ≤ n).
120 #m #n elim (nle_ge_e m n) [ /2 width=1 by or_introl/ ]
121 #Hnm elim (eq_nat_dec m n) [ #H destruct /2 width=1 by nle_refl, or_introl/ ]
122 /4 width=1 by nle_antisym, or_intror/