1 (* Equalities ***************************************************************)
3 lemma minus_plus_m_m_commutative: ∀n,m:nat. n = m + n - m.
6 lemma plus_minus_m_m_commutative (n) (m): m ≤ n → n = m+(n-m).
7 /2 width=1 by plus_minus_associative/ qed-.
9 lemma plus_to_minus_2: ∀m1,m2,n1,n2. n1 ≤ m1 → n2 ≤ m2 →
10 m1+n2 = m2+n1 → m1-n1 = m2-n2.
11 #m1 #m2 #n1 #n2 #H1 #H2 #H
12 @plus_to_minus >plus_minus_associative //
15 (* Note: uses minus_minus_comm, minus_plus_m_m, commutative_plus, plus_minus *)
16 lemma plus_minus_minus_be: ∀x,y,z. y ≤ z → z ≤ x → (x - z) + (z - y) = x - y.
17 #x #z #y #Hzy #Hyx >plus_minus // >commutative_plus >plus_minus //
20 lemma lt_succ_pred: ∀m,n. n < m → m = ↑↓m.
21 #m #n #Hm >S_pred /2 width=2 by ltn_to_ltO/
24 fact plus_minus_minus_be_aux: ∀i,x,y,z. y ≤ z → z ≤ x → i = z - y → x - z + i = x - y.
25 /2 width=1 by plus_minus_minus_be/ qed-.
27 lemma le_plus_minus: ∀m,n,p. p ≤ n → m + n - p = m + (n - p).
28 /2 by plus_minus/ qed-.
30 lemma le_plus_minus_comm: ∀n,m,p. p ≤ m → m + n - p = m - p + n.
31 /2 by plus_minus/ qed-.
33 lemma minus_minus_comm3: ∀n,x,y,z. n-x-y-z = n-y-z-x.
36 (* Properties ***************************************************************)
38 lemma eq_nat_dec: ∀n1,n2:nat. Decidable (n1 = n2).
39 #n1 elim n1 -n1 [| #n1 #IHn1 ] * [2,4: #n2 ]
40 [1,4: @or_intror #H destruct
41 | elim (IHn1 n2) -IHn1 /3 width=1 by or_intror, or_introl/
42 | /2 width=1 by or_introl/
46 lemma lt_or_eq_or_gt: ∀m,n. ∨∨ m < n | n = m | n < m.
47 #m #n elim (lt_or_ge m n) /2 width=1 by or3_intro0/
48 #H elim H -m /2 width=1 by or3_intro1/
49 #m #Hm * /3 width=1 by not_le_to_lt, le_S_S, or3_intro2/
52 lemma monotonic_le_minus_l2: ∀x1,x2,y,z. x1 ≤ x2 → x1 - y - z ≤ x2 - y - z.
53 /3 width=1 by monotonic_le_minus_l/ qed.
55 lemma minus_le_trans_sn: ∀x1,x2. x1 ≤ x2 → ∀x. x1-x ≤ x2.
56 /2 width=3 by transitive_le/ qed.
58 lemma le_plus_to_minus_l: ∀a,b,c. a + b ≤ c → b ≤ c-a.
59 /2 width=1 by le_plus_to_minus_r/
62 lemma le_plus_to_minus_comm: ∀n,m,p. n ≤ p+m → n-p ≤ m.
63 /2 width=1 by le_plus_to_minus/ qed-.
65 lemma le_inv_S1: ∀m,n. ↑m ≤ n → ∃∃p. m ≤ p & ↑p = n.
67 [ #H lapply (le_n_O_to_eq … H) -H
69 | /3 width=3 by monotonic_pred, ex2_intro/
73 (* Note: this might interfere with nat.ma *)
74 lemma monotonic_lt_pred: ∀m,n. m < n → 0 < m → pred m < pred n.
75 #m #n #Hmn #Hm whd >(S_pred … Hm)
76 @le_S_S_to_le >S_pred /2 width=3 by transitive_lt/
79 lemma lt_S_S: ∀x,y. x < y → ↑x < ↑y.
80 /2 width=1 by le_S_S/ qed.
82 lemma lt_S: ∀n,m. n < m → n < ↑m.
83 /2 width=1 by le_S/ qed.
85 lemma monotonic_lt_minus_r:
86 ∀p,q,n. q < n -> q < p → n-p < n-q.
88 lapply (monotonic_le_minus_r … n H) -H #H
89 @(le_to_lt_to_lt … H) -H
90 /2 width=1 by lt_plus_to_minus/
93 (* Inversion & forward lemmas ***********************************************)
95 lemma lt_refl_false: ∀n. n < n → ⊥.
96 #n #H elim (lt_to_not_eq … H) -H /2 width=1 by/
99 lemma lt_zero_false: ∀n. n < 0 → ⊥.
100 #n #H elim (lt_to_not_le … H) -H /2 width=1 by/
103 lemma lt_le_false: ∀x,y. x < y → y ≤ x → ⊥.
104 /3 width=4 by lt_refl_false, lt_to_le_to_lt/ qed-.
106 lemma le_dec (n) (m): Decidable (n≤m).
107 #n elim n -n [ /2 width=1 by or_introl/ ]
108 #n #IH * [ /3 width=2 by lt_zero_false, or_intror/ ]
110 [ /3 width=1 by or_introl, le_S_S/
111 | /4 width=1 by or_intror, le_S_S_to_le/
115 lemma succ_inv_refl_sn: ∀x. ↑x = x → ⊥.
116 #x #H @(lt_le_false x (↑x)) //
119 lemma le_plus_xSy_O_false: ∀x,y. x + S y ≤ 0 → ⊥.
120 #x #y #H lapply (le_n_O_to_eq … H) -H <plus_n_Sm #H destruct
123 lemma le_plus_xySz_x_false: ∀y,z,x. x + y + S z ≤ x → ⊥.
124 #y #z #x elim x -x /3 width=1 by le_S_S_to_le/
125 #H elim (le_plus_xSy_O_false … H)
128 lemma plus_xySz_x_false: ∀z,x,y. x + y + S z = x → ⊥.
129 /2 width=4 by le_plus_xySz_x_false/ qed-.
131 lemma plus_xSy_x_false: ∀y,x. x + S y = x → ⊥.
132 /2 width=4 by plus_xySz_x_false/ qed-.
134 lemma pred_inv_fix_sn: ∀x. ↓x = x → 0 = x.
136 elim (succ_inv_refl_sn x) //
139 lemma discr_plus_xy_y: ∀x,y. x + y = y → x = 0.
142 lemma discr_plus_x_xy: ∀x,y. x = x + y → y = 0.
143 /2 width=2 by le_plus_minus_comm/ qed-.
145 lemma plus2_le_sn_sn: ∀m1,m2,n1,n2. m1 + n1 = m2 + n2 → m1 ≤ m2 → n2 ≤ n1.
146 #m1 #m2 #n1 #n2 #H #Hm
147 lapply (monotonic_le_plus_l n1 … Hm) -Hm >H -H
148 /2 width=2 by le_plus_to_le/
151 lemma plus2_le_sn_dx: ∀m1,m2,n1,n2. m1 + n1 = n2 + m2 → m1 ≤ m2 → n2 ≤ n1.
152 /2 width=4 by plus2_le_sn_sn/ qed-.
154 lemma plus2_le_dx_sn: ∀m1,m2,n1,n2. n1 + m1 = m2 + n2 → m1 ≤ m2 → n2 ≤ n1.
155 /2 width=4 by plus2_le_sn_sn/ qed-.
157 lemma plus2_le_dx_dx: ∀m1,m2,n1,n2. n1 + m1 = n2 + m2 → m1 ≤ m2 → n2 ≤ n1.
158 /2 width=4 by plus2_le_sn_sn/ qed-.
160 lemma lt_S_S_to_lt: ∀x,y. ↑x < ↑y → x < y.
161 /2 width=1 by le_S_S_to_le/ qed-.
163 (* Note this should go in nat.ma *)
164 lemma discr_x_minus_xy: ∀x,y. x = x - y → x = 0 ∨ y = 0.
165 #x @(nat_ind_plus … x) -x /2 width=1 by or_introl/
166 #x #_ #y @(nat_ind_plus … y) -y /2 width=1 by or_intror/
167 #y #_ >minus_plus_plus_l
168 #H lapply (discr_plus_xy_minus_xz … H) -H
172 lemma lt_inv_O1: ∀n. 0 < n → ∃m. ↑m = n.
173 * /2 width=2 by ex_intro/
174 #H cases (lt_le_false … H) -H //
177 lemma lt_inv_S1: ∀m,n. ↑m < n → ∃∃p. m < p & ↑p = n.
178 #m * /3 width=3 by lt_S_S_to_lt, ex2_intro/
179 #H cases (lt_le_false … H) -H //
182 lemma lt_inv_gen: ∀y,x. x < y → ∃∃z. x ≤ z & ↑z = y.
183 * /3 width=3 by le_S_S_to_le, ex2_intro/
184 #x #H elim (lt_le_false … H) -H //
187 lemma plus_inv_O3: ∀x,y. x + y = 0 → x = 0 ∧ y = 0.
188 /2 width=1 by plus_le_0/ qed-.
190 lemma plus_inv_S3_sn: ∀x1,x2,x3. x1+x2 = ↑x3 →
191 ∨∨ ∧∧ x1 = 0 & x2 = ↑x3
192 | ∃∃y1. x1 = ↑y1 & y1 + x2 = x3.
193 * /3 width=1 by or_introl, conj/
194 #x1 #x2 #x3 <plus_S1 #H destruct
195 /3 width=3 by ex2_intro, or_intror/
198 lemma plus_inv_S3_dx: ∀x2,x1,x3. x1+x2 = ↑x3 →
199 ∨∨ ∧∧ x2 = 0 & x1 = ↑x3
200 | ∃∃y2. x2 = ↑y2 & x1 + y2 = x3.
201 * /3 width=1 by or_introl, conj/
202 #x2 #x1 #x3 <plus_n_Sm #H destruct
203 /3 width=3 by ex2_intro, or_intror/
206 lemma zero_eq_plus: ∀x,y. 0 = x + y → 0 = x ∧ 0 = y.
207 * /2 width=1 by conj/ #x #y normalize #H destruct
210 lemma nat_split: ∀x. x = 0 ∨ ∃y. ↑y = x.
211 * /3 width=2 by ex_intro, or_introl, or_intror/
214 lemma nat_elim_le_sn (Q:relation …):
215 (∀m1,m2. (∀m. m < m2-m1 → Q (m2-m) m2) → m1 ≤ m2 → Q m1 m2) →
216 ∀n1,n2. n1 ≤ n2 → Q n1 n2.
218 <(minus_minus_m_m … Hn) -Hn
219 lapply (minus_le n2 n1)
221 @(nat_elim1 … d) -d -n1 #d
223 <(minus_minus_m_m … Hd) in ⊢ (%→?); -Hd
225 @IH -IH [| // ] #m #Hn
226 /4 width=3 by lt_to_le, lt_to_le_to_lt/
229 (* Decidability of predicates ***********************************************)
231 lemma dec_lt (R:predicate nat):
232 (∀n. Decidable … (R n)) →
233 ∀n. Decidable … (∃∃m. m < n & R m).
234 #R #HR #n elim n -n [| #n * ]
235 [ @or_intror * /2 width=2 by lt_zero_false/
236 | * /4 width=3 by lt_S, or_introl, ex2_intro/
237 | #H0 elim (HR n) -HR
238 [ /3 width=3 by or_introl, ex2_intro/
239 | #Hn @or_intror * #m #Hmn #Hm
240 elim (le_to_or_lt_eq … Hmn) -Hmn #H destruct [ -Hn | -H0 ]
241 /4 width=3 by lt_S_S_to_lt, ex2_intro/
246 lemma dec_min (R:predicate nat):
247 (∀n. Decidable … (R n)) → ∀n. R n →
248 ∃∃m. m ≤ n & R m & (∀p. p < m → R p → ⊥).
250 @(nat_elim1 n) -n #n #IH #Hn
251 elim (dec_lt … HR n) -HR [ -Hn | -IH ]
253 elim (IH … Hpn Hp) -IH -Hp #m #Hmp #Hm #HNm
254 @(ex3_intro … Hm HNm) -HNm
255 /3 width=3 by lt_to_le, le_to_lt_to_lt/
256 | /4 width=4 by ex3_intro, ex2_intro/