numbers.v 22.5 KB
Newer Older
Robbert Krebbers's avatar
Robbert Krebbers committed
1 2 3 4 5
(* Copyright (c) 2012-2015, Robbert Krebbers. *)
(* This file is distributed under the terms of the BSD license. *)
(** This file collects some trivial facts on the Coq types [nat] and [N] for
natural numbers, and the type [Z] for integers. It also declares some useful
notations. *)
6
From Coq Require Export EqdepFacts PArith NArith ZArith NPeano.
7
From Coq Require Import QArith Qcanon.
8
From iris.prelude Require Export base decidable option.
Robbert Krebbers's avatar
Robbert Krebbers committed
9 10 11
Open Scope nat_scope.

Coercion Z.of_nat : nat >-> Z.
12
Instance comparison_eq_dec : EqDecision comparison.
13
Proof. solve_decision. Defined.
Robbert Krebbers's avatar
Robbert Krebbers committed
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

(** * Notations and properties of [nat] *)
Arguments minus !_ !_ /.
Reserved Notation "x ≤ y ≤ z" (at level 70, y at next level).
Reserved Notation "x ≤ y < z" (at level 70, y at next level).
Reserved Notation "x < y < z" (at level 70, y at next level).
Reserved Notation "x < y ≤ z" (at level 70, y at next level).
Reserved Notation "x ≤ y ≤ z ≤ z'"
  (at level 70, y at next level, z at next level).

Infix "≤" := le : nat_scope.
Notation "x ≤ y ≤ z" := (x  y  y  z)%nat : nat_scope.
Notation "x ≤ y < z" := (x  y  y < z)%nat : nat_scope.
Notation "x < y < z" := (x < y  y < z)%nat : nat_scope.
Notation "x < y ≤ z" := (x < y  y  z)%nat : nat_scope.
Notation "x ≤ y ≤ z ≤ z'" := (x  y  y  z  z  z')%nat : nat_scope.
Notation "(≤)" := le (only parsing) : nat_scope.
Notation "(<)" := lt (only parsing) : nat_scope.

Infix "`div`" := Nat.div (at level 35) : nat_scope.
Infix "`mod`" := Nat.modulo (at level 35) : nat_scope.
Robbert Krebbers's avatar
Robbert Krebbers committed
35 36
Infix "`max`" := Nat.max (at level 35) : nat_scope.
Infix "`min`" := Nat.min (at level 35) : nat_scope.
Robbert Krebbers's avatar
Robbert Krebbers committed
37

38
Instance nat_eq_dec: EqDecision nat := eq_nat_dec.
Robbert Krebbers's avatar
Robbert Krebbers committed
39 40 41
Instance nat_le_dec:  x y : nat, Decision (x  y) := le_dec.
Instance nat_lt_dec:  x y : nat, Decision (x < y) := lt_dec.
Instance nat_inhabited: Inhabited nat := populate 0%nat.
42
Instance S_inj: Inj (=) (=) S.
Robbert Krebbers's avatar
Robbert Krebbers committed
43
Proof. by injection 1. Qed.
44
Instance nat_le_po: PartialOrder ().
Robbert Krebbers's avatar
Robbert Krebbers committed
45 46 47 48 49 50 51
Proof. repeat split; repeat intro; auto with lia. Qed.

Instance nat_le_pi:  x y : nat, ProofIrrel (x  y).
Proof.
  assert ( x y (p : x  y) y' (q : x  y'),
    y = y'  eq_dep nat (le x) y p y' q) as aux.
  { fix 3. intros x ? [|y p] ? [|y' q].
52 53 54 55
    - done.
    - clear nat_le_pi. intros; exfalso; auto with lia.
    - clear nat_le_pi. intros; exfalso; auto with lia.
    - injection 1. intros Hy. by case (nat_le_pi x y p y' q Hy). }
Robbert Krebbers's avatar
Robbert Krebbers committed
56
  intros x y p q.
57
  by apply (Eqdep_dec.eq_dep_eq_dec (λ x y, decide (x = y))), aux.
Robbert Krebbers's avatar
Robbert Krebbers committed
58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84
Qed.
Instance nat_lt_pi:  x y : nat, ProofIrrel (x < y).
Proof. apply _. Qed.

Definition sum_list_with {A} (f : A  nat) : list A  nat :=
  fix go l :=
  match l with
  | [] => 0
  | x :: l => f x + go l
  end.
Notation sum_list := (sum_list_with id).

Lemma Nat_lt_succ_succ n : n < S (S n).
Proof. auto with arith. Qed.
Lemma Nat_mul_split_l n x1 x2 y1 y2 :
  x2 < n  y2 < n  x1 * n + x2 = y1 * n + y2  x1 = y1  x2 = y2.
Proof.
  intros Hx2 Hy2 E. cut (x1 = y1); [intros; subst;lia |].
  revert y1 E. induction x1; simpl; intros [|?]; simpl; auto with lia.
Qed.
Lemma Nat_mul_split_r n x1 x2 y1 y2 :
  x1 < n  y1 < n  x1 + x2 * n = y1 + y2 * n  x1 = y1  x2 = y2.
Proof. intros. destruct (Nat_mul_split_l n x2 x1 y2 y1); auto with lia. Qed.

Notation lcm := Nat.lcm.
Notation divide := Nat.divide.
Notation "( x | y )" := (divide x y) : nat_scope.
85
Instance Nat_divide_dec x y : Decision (x | y).
Robbert Krebbers's avatar
Robbert Krebbers committed
86 87 88 89 90 91 92 93 94 95 96
Proof.
  refine (cast_if (decide (lcm x y = y))); by rewrite Nat.divide_lcm_iff.
Defined.
Instance: PartialOrder divide.
Proof.
  repeat split; try apply _. intros ??. apply Nat.divide_antisym_nonneg; lia.
Qed.
Hint Extern 0 (_ | _) => reflexivity.
Lemma Nat_divide_ne_0 x y : (x | y)  y  0  x  0.
Proof. intros Hxy Hy ->. by apply Hy, Nat.divide_0_l. Qed.

97 98 99 100 101
Lemma Nat_iter_S {A} n (f: A  A) x : Nat.iter (S n) f x = f (Nat.iter n f x).
Proof. done. Qed.
Lemma Nat_iter_S_r {A} n (f: A  A) x : Nat.iter (S n) f x = Nat.iter n f (f x).
Proof. induction n; f_equal/=; auto. Qed.

Robbert Krebbers's avatar
Robbert Krebbers committed
102 103 104 105 106 107 108 109 110 111 112 113 114 115
(** * Notations and properties of [positive] *)
Open Scope positive_scope.

Infix "≤" := Pos.le : positive_scope.
Notation "x ≤ y ≤ z" := (x  y  y  z) : positive_scope.
Notation "x ≤ y < z" := (x  y  y < z) : positive_scope.
Notation "x < y < z" := (x < y  y < z) : positive_scope.
Notation "x < y ≤ z" := (x < y  y  z) : positive_scope.
Notation "x ≤ y ≤ z ≤ z'" := (x  y  y  z  z  z') : positive_scope.
Notation "(≤)" := Pos.le (only parsing) : positive_scope.
Notation "(<)" := Pos.lt (only parsing) : positive_scope.
Notation "(~0)" := xO (only parsing) : positive_scope.
Notation "(~1)" := xI (only parsing) : positive_scope.

116 117 118
Arguments Pos.of_nat : simpl never.
Arguments Pmult : simpl never.

119
Instance positive_eq_dec: EqDecision positive := Pos.eq_dec.
Robbert Krebbers's avatar
Robbert Krebbers committed
120 121
Instance positive_inhabited: Inhabited positive := populate 1.

122 123
Instance maybe_xO : Maybe xO := λ p, match p with p~0 => Some p | _ => None end.
Instance maybe_x1 : Maybe xI := λ p, match p with p~1 => Some p | _ => None end.
124
Instance: Inj (=) (=) (~0).
Robbert Krebbers's avatar
Robbert Krebbers committed
125
Proof. by injection 1. Qed.
126
Instance: Inj (=) (=) (~1).
Robbert Krebbers's avatar
Robbert Krebbers committed
127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151
Proof. by injection 1. Qed.

(** Since [positive] represents lists of bits, we define list operations
on it. These operations are in reverse, as positives are treated as snoc
lists instead of cons lists. *)
Fixpoint Papp (p1 p2 : positive) : positive :=
  match p2 with
  | 1 => p1
  | p2~0 => (Papp p1 p2)~0
  | p2~1 => (Papp p1 p2)~1
  end.
Infix "++" := Papp : positive_scope.
Notation "(++)" := Papp (only parsing) : positive_scope.
Notation "( p ++)" := (Papp p) (only parsing) : positive_scope.
Notation "(++ q )" := (λ p, Papp p q) (only parsing) : positive_scope.

Fixpoint Preverse_go (p1 p2 : positive) : positive :=
  match p2 with
  | 1 => p1
  | p2~0 => Preverse_go (p1~0) p2
  | p2~1 => Preverse_go (p1~1) p2
  end.
Definition Preverse : positive  positive := Preverse_go 1.

Global Instance: LeftId (=) 1 (++).
152
Proof. intros p. by induction p; intros; f_equal/=. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
153 154
Global Instance: RightId (=) 1 (++).
Proof. done. Qed.
155
Global Instance: Assoc (=) (++).
156
Proof. intros ?? p. by induction p; intros; f_equal/=. Qed.
157
Global Instance:  p : positive, Inj (=) (=) (++ p).
158
Proof. intros p ???. induction p; simplify_eq; auto. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
159 160 161 162

Lemma Preverse_go_app p1 p2 p3 :
  Preverse_go p1 (p2 ++ p3) = Preverse_go p1 p3 ++ Preverse_go 1 p2.
Proof.
163 164 165 166
  revert p3 p1 p2.
  cut ( p1 p2 p3, Preverse_go (p2 ++ p3) p1 = p2 ++ Preverse_go p3 p1).
  { by intros go p3; induction p3; intros p1 p2; simpl; auto; rewrite <-?go. }
  intros p1; induction p1 as [p1 IH|p1 IH|]; intros p2 p3; simpl; auto.
167 168
  - apply (IH _ (_~1)).
  - apply (IH _ (_~0)).
Robbert Krebbers's avatar
Robbert Krebbers committed
169
Qed.
170
Lemma Preverse_app p1 p2 : Preverse (p1 ++ p2) = Preverse p2 ++ Preverse p1.
Robbert Krebbers's avatar
Robbert Krebbers committed
171 172 173 174 175 176 177 178
Proof. unfold Preverse. by rewrite Preverse_go_app. Qed.
Lemma Preverse_xO p : Preverse (p~0) = (1~0) ++ Preverse p.
Proof Preverse_app p (1~0).
Lemma Preverse_xI p : Preverse (p~1) = (1~1) ++ Preverse p.
Proof Preverse_app p (1~1).

Fixpoint Plength (p : positive) : nat :=
  match p with 1 => 0%nat | p~0 | p~1 => S (Plength p) end.
179
Lemma Papp_length p1 p2 : Plength (p1 ++ p2) = (Plength p2 + Plength p1)%nat.
180
Proof. by induction p2; f_equal/=. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197

Close Scope positive_scope.

(** * Notations and properties of [N] *)
Infix "≤" := N.le : N_scope.
Notation "x ≤ y ≤ z" := (x  y  y  z)%N : N_scope.
Notation "x ≤ y < z" := (x  y  y < z)%N : N_scope.
Notation "x < y < z" := (x < y  y < z)%N : N_scope.
Notation "x < y ≤ z" := (x < y  y  z)%N : N_scope.
Notation "x ≤ y ≤ z ≤ z'" := (x  y  y  z  z  z')%N : N_scope.
Notation "(≤)" := N.le (only parsing) : N_scope.
Notation "(<)" := N.lt (only parsing) : N_scope.
Infix "`div`" := N.div (at level 35) : N_scope.
Infix "`mod`" := N.modulo (at level 35) : N_scope.

Arguments N.add _ _ : simpl never.

198
Instance: Inj (=) (=) Npos.
Robbert Krebbers's avatar
Robbert Krebbers committed
199 200
Proof. by injection 1. Qed.

201
Instance N_eq_dec: EqDecision N := N.eq_dec.
Robbert Krebbers's avatar
Robbert Krebbers committed
202
Program Instance N_le_dec (x y : N) : Decision (x  y)%N :=
203 204
  match Ncompare x y with Gt => right _ | _ => left _ end.
Solve Obligations with naive_solver.
Robbert Krebbers's avatar
Robbert Krebbers committed
205
Program Instance N_lt_dec (x y : N) : Decision (x < y)%N :=
206 207
  match Ncompare x y with Lt => left _ | _ => right _ end.
Solve Obligations with naive_solver.
Robbert Krebbers's avatar
Robbert Krebbers committed
208
Instance N_inhabited: Inhabited N := populate 1%N.
209
Instance N_le_po: PartialOrder ()%N.
Robbert Krebbers's avatar
Robbert Krebbers committed
210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233
Proof.
  repeat split; red. apply N.le_refl. apply N.le_trans. apply N.le_antisymm.
Qed.
Hint Extern 0 (_  _)%N => reflexivity.

(** * Notations and properties of [Z] *)
Open Scope Z_scope.

Infix "≤" := Z.le : Z_scope.
Notation "x ≤ y ≤ z" := (x  y  y  z) : Z_scope.
Notation "x ≤ y < z" := (x  y  y < z) : Z_scope.
Notation "x < y < z" := (x < y  y < z) : Z_scope.
Notation "x < y ≤ z" := (x < y  y  z) : Z_scope.
Notation "x ≤ y ≤ z ≤ z'" := (x  y  y  z  z  z') : Z_scope.
Notation "(≤)" := Z.le (only parsing) : Z_scope.
Notation "(<)" := Z.lt (only parsing) : Z_scope.

Infix "`div`" := Z.div (at level 35) : Z_scope.
Infix "`mod`" := Z.modulo (at level 35) : Z_scope.
Infix "`quot`" := Z.quot (at level 35) : Z_scope.
Infix "`rem`" := Z.rem (at level 35) : Z_scope.
Infix "≪" := Z.shiftl (at level 35) : Z_scope.
Infix "≫" := Z.shiftr (at level 35) : Z_scope.

234
Instance Zpos_inj : Inj (=) (=) Zpos.
Robbert Krebbers's avatar
Robbert Krebbers committed
235
Proof. by injection 1. Qed.
236
Instance Zneg_inj : Inj (=) (=) Zneg.
Robbert Krebbers's avatar
Robbert Krebbers committed
237 238
Proof. by injection 1. Qed.

239 240 241
Instance Z_of_nat_inj : Inj (=) (=) Z.of_nat.
Proof. intros n1 n2. apply Nat2Z.inj. Qed.

242
Instance Z_eq_dec: EqDecision Z := Z.eq_dec.
Robbert Krebbers's avatar
Robbert Krebbers committed
243 244 245
Instance Z_le_dec:  x y : Z, Decision (x  y) := Z_le_dec.
Instance Z_lt_dec:  x y : Z, Decision (x < y) := Z_lt_dec.
Instance Z_inhabited: Inhabited Z := populate 1.
246
Instance Z_le_po : PartialOrder ().
Robbert Krebbers's avatar
Robbert Krebbers committed
247 248 249 250 251 252 253 254 255 256 257 258 259
Proof.
  repeat split; red. apply Z.le_refl. apply Z.le_trans. apply Z.le_antisymm.
Qed.

Lemma Z_pow_pred_r n m : 0 < m  n * n ^ (Z.pred m) = n ^ m.
Proof.
  intros. rewrite <-Z.pow_succ_r, Z.succ_pred. done. by apply Z.lt_le_pred.
Qed.
Lemma Z_quot_range_nonneg k x y : 0  x < k  0 < y  0  x `quot` y < k.
Proof.
  intros [??] ?.
  destruct (decide (y = 1)); subst; [rewrite Z.quot_1_r; auto |].
  destruct (decide (x = 0)); subst; [rewrite Z.quot_0_l; auto with lia |].
260
  split. apply Z.quot_pos; lia. trans x; auto. apply Z.quot_lt; lia.
Robbert Krebbers's avatar
Robbert Krebbers committed
261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299
Qed.

(* Note that we cannot disable simpl for [Z.of_nat] as that would break
tactics as [lia]. *)
Arguments Z.to_nat _ : simpl never.
Arguments Z.mul _ _ : simpl never.
Arguments Z.add _ _ : simpl never.
Arguments Z.opp _ : simpl never.
Arguments Z.pow _ _ : simpl never.
Arguments Z.div _ _ : simpl never.
Arguments Z.modulo _ _ : simpl never.
Arguments Z.quot _ _ : simpl never.
Arguments Z.rem _ _ : simpl never.

Lemma Z_to_nat_neq_0_pos x : Z.to_nat x  0%nat  0 < x.
Proof. by destruct x. Qed.
Lemma Z_to_nat_neq_0_nonneg x : Z.to_nat x  0%nat  0  x.
Proof. by destruct x. Qed.
Lemma Z_mod_pos x y : 0 < y  0  x `mod` y.
Proof. apply Z.mod_pos_bound. Qed.

Hint Resolve Z.lt_le_incl : zpos.
Hint Resolve Z.add_nonneg_pos Z.add_pos_nonneg Z.add_nonneg_nonneg : zpos.
Hint Resolve Z.mul_nonneg_nonneg Z.mul_pos_pos : zpos.
Hint Resolve Z.pow_pos_nonneg Z.pow_nonneg: zpos.
Hint Resolve Z_mod_pos Z.div_pos : zpos.
Hint Extern 1000 => lia : zpos.

Lemma Z_to_nat_nonpos x : x  0  Z.to_nat x = 0%nat.
Proof. destruct x; simpl; auto using Z2Nat.inj_neg. by intros []. Qed.
Lemma Z2Nat_inj_pow (x y : nat) : Z.of_nat (x ^ y) = x ^ y.
Proof.
  induction y as [|y IH]; [by rewrite Z.pow_0_r, Nat.pow_0_r|].
  by rewrite Nat.pow_succ_r, Nat2Z.inj_succ, Z.pow_succ_r,
    Nat2Z.inj_mul, IH by auto with zpos.
Qed.
Lemma Nat2Z_divide n m : (Z.of_nat n | Z.of_nat m)  (n | m)%nat.
Proof.
  split.
300
  - rewrite <-(Nat2Z.id m) at 2; intros [i ->]; exists (Z.to_nat i).
Robbert Krebbers's avatar
Robbert Krebbers committed
301 302 303
    destruct (decide (0  i)%Z).
    { by rewrite Z2Nat.inj_mul, Nat2Z.id by lia. }
    by rewrite !Z_to_nat_nonpos by auto using Z.mul_nonpos_nonneg with lia.
304
  - intros [i ->]. exists (Z.of_nat i). by rewrite Nat2Z.inj_mul.
Robbert Krebbers's avatar
Robbert Krebbers committed
305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347
Qed.
Lemma Z2Nat_divide n m :
  0  n  0  m  (Z.to_nat n | Z.to_nat m)%nat  (n | m).
Proof. intros. by rewrite <-Nat2Z_divide, !Z2Nat.id by done. Qed.
Lemma Z2Nat_inj_div x y : Z.of_nat (x `div` y) = x `div` y.
Proof.
  destruct (decide (y = 0%nat)); [by subst; destruct x |].
  apply Z.div_unique with (x `mod` y)%nat.
  { left. rewrite <-(Nat2Z.inj_le 0), <-Nat2Z.inj_lt.
    apply Nat.mod_bound_pos; lia. }
  by rewrite <-Nat2Z.inj_mul, <-Nat2Z.inj_add, <-Nat.div_mod.
Qed.
Lemma Z2Nat_inj_mod x y : Z.of_nat (x `mod` y) = x `mod` y.
Proof.
  destruct (decide (y = 0%nat)); [by subst; destruct x |].
  apply Z.mod_unique with (x `div` y)%nat.
  { left. rewrite <-(Nat2Z.inj_le 0), <-Nat2Z.inj_lt.
    apply Nat.mod_bound_pos; lia. }
  by rewrite <-Nat2Z.inj_mul, <-Nat2Z.inj_add, <-Nat.div_mod.
Qed.
Close Scope Z_scope.

(** * Notations and properties of [Qc] *)
Open Scope Qc_scope.
Delimit Scope Qc_scope with Qc.
Notation "1" := (Q2Qc 1) : Qc_scope.
Notation "2" := (1+1) : Qc_scope.
Notation "- 1" := (Qcopp 1) : Qc_scope.
Notation "- 2" := (Qcopp 2) : Qc_scope.
Notation "x - y" := (x + -y) : Qc_scope.
Notation "x / y" := (x * /y) : Qc_scope.
Infix "≤" := Qcle : Qc_scope.
Notation "x ≤ y ≤ z" := (x  y  y  z) : Qc_scope.
Notation "x ≤ y < z" := (x  y  y < z) : Qc_scope.
Notation "x < y < z" := (x < y  y < z) : Qc_scope.
Notation "x < y ≤ z" := (x < y  y  z) : Qc_scope.
Notation "x ≤ y ≤ z ≤ z'" := (x  y  y  z  z  z') : Qc_scope.
Notation "(≤)" := Qcle (only parsing) : Qc_scope.
Notation "(<)" := Qclt (only parsing) : Qc_scope.

Hint Extern 1 (_  _) => reflexivity || discriminate.
Arguments Qred _ : simpl never.

348
Instance Qc_eq_dec: EqDecision Qc := Qc_eq_dec.
Robbert Krebbers's avatar
Robbert Krebbers committed
349 350
Program Instance Qc_le_dec (x y : Qc) : Decision (x  y) :=
  if Qclt_le_dec y x then right _ else left _.
351 352
Next Obligation. intros x y; apply Qclt_not_le. Qed.
Next Obligation. done. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
353 354
Program Instance Qc_lt_dec (x y : Qc) : Decision (x < y) :=
  if Qclt_le_dec x y then left _ else right _.
355 356
Solve Obligations with done.
Next Obligation. intros x y; apply Qcle_not_lt. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
357 358 359 360 361 362 363 364 365 366 367 368 369

Instance: PartialOrder ().
Proof.
  repeat split; red. apply Qcle_refl. apply Qcle_trans. apply Qcle_antisym.
Qed.
Instance: StrictOrder (<).
Proof.
  split; red. intros x Hx. by destruct (Qclt_not_eq x x). apply Qclt_trans.
Qed.
Lemma Qcmult_0_l x : 0 * x = 0.
Proof. ring. Qed.
Lemma Qcmult_0_r x : x * 0 = 0.
Proof. ring. Qed.
370 371
Lemma Qcplus_diag x : (x + x)%Qc = (2 * x)%Qc.
Proof. ring. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
372 373 374 375 376 377 378
Lemma Qcle_ngt (x y : Qc) : x  y  ¬y < x.
Proof. split; auto using Qcle_not_lt, Qcnot_lt_le. Qed.
Lemma Qclt_nge (x y : Qc) : x < y  ¬y  x.
Proof. split; auto using Qclt_not_le, Qcnot_le_lt. Qed.
Lemma Qcplus_le_mono_l (x y z : Qc) : x  y  z + x  z + y.
Proof.
  split; intros.
379 380
  - by apply Qcplus_le_compat.
  - replace x with ((0 - z) + (z + x)) by ring.
Robbert Krebbers's avatar
Robbert Krebbers committed
381 382 383 384 385 386 387 388 389
    replace y with ((0 - z) + (z + y)) by ring.
    by apply Qcplus_le_compat.
Qed.
Lemma Qcplus_le_mono_r (x y z : Qc) : x  y  x + z  y + z.
Proof. rewrite !(Qcplus_comm _ z). apply Qcplus_le_mono_l. Qed.
Lemma Qcplus_lt_mono_l (x y z : Qc) : x < y  z + x < z + y.
Proof. by rewrite !Qclt_nge, <-Qcplus_le_mono_l. Qed.
Lemma Qcplus_lt_mono_r (x y z : Qc) : x < y  x + z < y + z.
Proof. by rewrite !Qclt_nge, <-Qcplus_le_mono_r. Qed.
390
Instance: Inj (=) (=) Qcopp.
Robbert Krebbers's avatar
Robbert Krebbers committed
391 392 393
Proof.
  intros x y H. by rewrite <-(Qcopp_involutive x), H, Qcopp_involutive.
Qed.
394
Instance:  z, Inj (=) (=) (Qcplus z).
Robbert Krebbers's avatar
Robbert Krebbers committed
395
Proof.
396
  intros z x y H. by apply (anti_symm ());
Robbert Krebbers's avatar
Robbert Krebbers committed
397 398
    rewrite (Qcplus_le_mono_l _ _ z), H.
Qed.
399
Instance:  z, Inj (=) (=) (λ x, x + z).
Robbert Krebbers's avatar
Robbert Krebbers committed
400
Proof.
401
  intros z x y H. by apply (anti_symm ());
Robbert Krebbers's avatar
Robbert Krebbers committed
402 403 404 405 406 407 408 409 410 411 412 413 414
    rewrite (Qcplus_le_mono_r _ _ z), H.
Qed.
Lemma Qcplus_pos_nonneg (x y : Qc) : 0 < x  0  y  0 < x + y.
Proof.
  intros. apply Qclt_le_trans with (x + 0); [by rewrite Qcplus_0_r|].
  by apply Qcplus_le_mono_l.
Qed.
Lemma Qcplus_nonneg_pos (x y : Qc) : 0  x  0 < y  0 < x + y.
Proof. rewrite (Qcplus_comm x). auto using Qcplus_pos_nonneg. Qed. 
Lemma Qcplus_pos_pos (x y : Qc) : 0 < x  0 < y  0 < x + y.
Proof. auto using Qcplus_pos_nonneg, Qclt_le_weak. Qed.
Lemma Qcplus_nonneg_nonneg (x y : Qc) : 0  x  0  y  0  x + y.
Proof.
415
  intros. trans (x + 0); [by rewrite Qcplus_0_r|].
Robbert Krebbers's avatar
Robbert Krebbers committed
416 417 418 419 420 421 422 423 424 425 426 427 428
  by apply Qcplus_le_mono_l.
Qed.
Lemma Qcplus_neg_nonpos (x y : Qc) : x < 0  y  0  x + y < 0.
Proof.
  intros. apply Qcle_lt_trans with (x + 0); [|by rewrite Qcplus_0_r].
  by apply Qcplus_le_mono_l.
Qed.
Lemma Qcplus_nonpos_neg (x y : Qc) : x  0  y < 0  x + y < 0.
Proof. rewrite (Qcplus_comm x). auto using Qcplus_neg_nonpos. Qed.
Lemma Qcplus_neg_neg (x y : Qc) : x < 0  y < 0  x + y < 0.
Proof. auto using Qcplus_nonpos_neg, Qclt_le_weak. Qed.
Lemma Qcplus_nonpos_nonpos (x y : Qc) : x  0  y  0  x + y  0.
Proof.
429
  intros. trans (x + 0); [|by rewrite Qcplus_0_r].
Robbert Krebbers's avatar
Robbert Krebbers committed
430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454
  by apply Qcplus_le_mono_l.
Qed.
Lemma Qcmult_le_mono_nonneg_l x y z : 0  z  x  y  z * x  z * y.
Proof. intros. rewrite !(Qcmult_comm z). by apply Qcmult_le_compat_r. Qed.
Lemma Qcmult_le_mono_nonneg_r x y z : 0  z  x  y  x * z  y * z.
Proof. intros. by apply Qcmult_le_compat_r. Qed.
Lemma Qcmult_le_mono_pos_l x y z : 0 < z  x  y  z * x  z * y.
Proof.
  split; auto using Qcmult_le_mono_nonneg_l, Qclt_le_weak.
  rewrite !Qcle_ngt, !(Qcmult_comm z).
  intuition auto using Qcmult_lt_compat_r.
Qed.
Lemma Qcmult_le_mono_pos_r x y z : 0 < z  x  y  x * z  y * z.
Proof. rewrite !(Qcmult_comm _ z). by apply Qcmult_le_mono_pos_l. Qed.
Lemma Qcmult_lt_mono_pos_l x y z : 0 < z  x < y  z * x < z * y.
Proof. intros. by rewrite !Qclt_nge, <-Qcmult_le_mono_pos_l. Qed.
Lemma Qcmult_lt_mono_pos_r x y z : 0 < z  x < y  x * z < y * z.
Proof. intros. by rewrite !Qclt_nge, <-Qcmult_le_mono_pos_r. Qed.
Lemma Qcmult_pos_pos x y : 0 < x  0 < y  0 < x * y.
Proof.
  intros. apply Qcle_lt_trans with (0 * y); [by rewrite Qcmult_0_l|].
  by apply Qcmult_lt_mono_pos_r.
Qed.
Lemma Qcmult_nonneg_nonneg x y : 0  x  0  y  0  x * y.
Proof.
455
  intros. trans (0 * y); [by rewrite Qcmult_0_l|].
Robbert Krebbers's avatar
Robbert Krebbers committed
456 457 458 459 460 461 462 463
  by apply Qcmult_le_mono_nonneg_r.
Qed.

Lemma inject_Z_Qred n : Qred (inject_Z n) = inject_Z n.
Proof. apply Qred_identity; auto using Z.gcd_1_r. Qed.
Coercion Qc_of_Z (n : Z) : Qc := Qcmake _ (inject_Z_Qred n).
Lemma Z2Qc_inj_0 : Qc_of_Z 0 = 0.
Proof. by apply Qc_is_canon. Qed.
464 465 466 467
Lemma Z2Qc_inj_1 : Qc_of_Z 1 = 1.
Proof. by apply Qc_is_canon. Qed.
Lemma Z2Qc_inj_2 : Qc_of_Z 2 = 2.
Proof. by apply Qc_is_canon. Qed.
Robbert Krebbers's avatar
Robbert Krebbers committed
468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487
Lemma Z2Qc_inj n m : Qc_of_Z n = Qc_of_Z m  n = m.
Proof. by injection 1. Qed.
Lemma Z2Qc_inj_iff n m : Qc_of_Z n = Qc_of_Z m  n = m.
Proof. split. auto using Z2Qc_inj. by intros ->. Qed.
Lemma Z2Qc_inj_le n m : (n  m)%Z  Qc_of_Z n  Qc_of_Z m.
Proof. by rewrite Zle_Qle. Qed.
Lemma Z2Qc_inj_lt n m : (n < m)%Z  Qc_of_Z n < Qc_of_Z m.
Proof. by rewrite Zlt_Qlt. Qed.
Lemma Z2Qc_inj_add n m : Qc_of_Z (n + m) = Qc_of_Z n + Qc_of_Z m.
Proof. apply Qc_is_canon; simpl. by rewrite Qred_correct, inject_Z_plus. Qed.
Lemma Z2Qc_inj_mul n m : Qc_of_Z (n * m) = Qc_of_Z n * Qc_of_Z m.
Proof. apply Qc_is_canon; simpl. by rewrite Qred_correct, inject_Z_mult. Qed.
Lemma Z2Qc_inj_opp n : Qc_of_Z (-n) = -Qc_of_Z n.
Proof. apply Qc_is_canon; simpl. by rewrite Qred_correct, inject_Z_opp. Qed.
Lemma Z2Qc_inj_sub n m : Qc_of_Z (n - m) = Qc_of_Z n - Qc_of_Z m.
Proof.
  apply Qc_is_canon; simpl.
  by rewrite !Qred_correct, <-inject_Z_opp, <-inject_Z_plus.
Qed.
Close Scope Qc_scope.
488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516

(** * Positive rationals *)
(** The theory of positive rationals is very incomplete. We merely provide
some operations and theorems that are relevant for fractional permissions. *)
Record Qp := mk_Qp { Qp_car :> Qc ; Qp_prf : (0 < Qp_car)%Qc }.
Hint Resolve Qp_prf.
Delimit Scope Qp_scope with Qp.
Bind Scope Qp_scope with Qp.
Arguments Qp_car _%Qp.

Definition Qp_one : Qp := mk_Qp 1 eq_refl.
Program Definition Qp_plus (x y : Qp) : Qp := mk_Qp (x + y) _.
Next Obligation. by intros x y; apply Qcplus_pos_pos. Qed.
Definition Qp_minus (x y : Qp) : option Qp :=
  let z := (x - y)%Qc in
  match decide (0 < z)%Qc with left Hz => Some (mk_Qp z Hz) | _ => None end.
Program Definition Qp_div (x : Qp) (y : positive) : Qp := mk_Qp (x / ('y)%Z) _.  
Next Obligation.
  intros x y. assert (0 < ('y)%Z)%Qc.
  { apply (Z2Qc_inj_lt 0%Z (' y)), Pos2Z.is_pos. }
  by rewrite (Qcmult_lt_mono_pos_r _ _ ('y)%Z), Qcmult_0_l,
    <-Qcmult_assoc, Qcmult_inv_l, Qcmult_1_r.
Qed.

Notation "1" := Qp_one : Qp_scope.
Infix "+" := Qp_plus : Qp_scope.
Infix "-" := Qp_minus : Qp_scope.
Infix "/" := Qp_div : Qp_scope.

Robbert Krebbers's avatar
Robbert Krebbers committed
517 518
Instance Qp_inhabited : Inhabited Qp := populate 1%Qp.

519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552
Lemma Qp_eq x y : x = y  Qp_car x = Qp_car y.
Proof.
  split; [by intros ->|].
  destruct x, y; intros; simplify_eq/=; f_equal; apply (proof_irrel _).
Qed.
Instance Qp_plus_assoc : Assoc (=) Qp_plus.
Proof. intros x y z; apply Qp_eq, Qcplus_assoc. Qed.
Instance Qp_plus_comm : Comm (=) Qp_plus.
Proof. intros x y; apply Qp_eq, Qcplus_comm. Qed.

Lemma Qp_minus_diag x : (x - x)%Qp = None.
Proof. unfold Qp_minus. by rewrite Qcplus_opp_r. Qed.
Lemma Qp_op_minus x y : ((x + y) - x)%Qp = Some y.
Proof.
  unfold Qp_minus; simpl.
  rewrite (Qcplus_comm x), <- Qcplus_assoc, Qcplus_opp_r, Qcplus_0_r.
  destruct (decide _) as [|[]]; auto. by f_equal; apply Qp_eq.
Qed.

Lemma Qp_div_1 x : (x / 1 = x)%Qp.
Proof.
  apply Qp_eq; simpl.
  rewrite <-(Qcmult_div_r x 1) at 2 by done. by rewrite Qcmult_1_l.
Qed.
Lemma Qp_div_S x y : (x / (2 * y) + x / (2 * y) = x / y)%Qp.
Proof.
  apply Qp_eq; simpl.
  rewrite <-Qcmult_plus_distr_l, Pos2Z.inj_mul, Z2Qc_inj_mul, Z2Qc_inj_2.
  rewrite Qcplus_diag. by field_simplify.
Qed.
Lemma Qp_div_2 x : (x / 2 + x / 2 = x)%Qp.
Proof.
  change 2%positive with (2 * 1)%positive. by rewrite Qp_div_S, Qp_div_1.
Qed.
553

554 555 556 557 558 559 560 561 562 563 564 565 566 567
Lemma Qp_lower_bound q1 q2 :  q q1' q2', (q1 = q + q1'  q2 = q + q2')%Qp.
Proof.
  revert q1 q2. cut ( q1 q2 : Qp, (q1  q2)%Qc 
     q q1' q2', (q1 = q + q1'  q2 = q + q2')%Qp).
  { intros help q1 q2.
    destruct (Qc_le_dec q1 q2) as [LE|LE%Qclt_nge%Qclt_le_weak]; [by eauto|].
    destruct (help q2 q1) as (q&q1'&q2'&?&?); eauto. }
  intros q1 q2 Hq. exists (q1 / 2)%Qp, (q1 / 2)%Qp.
  assert (0 < q2 - q1 / 2)%Qc as Hq2'.
  { eapply Qclt_le_trans; [|by apply Qcplus_le_mono_r, Hq].
    replace (q1 - q1 / 2)%Qc with (q1 * (1 - 1/2))%Qc by ring.
    replace 0%Qc with (0 * (1-1/2))%Qc by ring. by apply Qcmult_lt_compat_r. }
  exists (mk_Qp (q2 - q1 / 2%Z) Hq2'). split; [by rewrite Qp_div_2|].
  apply Qp_eq; simpl. ring.
568
Qed.
569

Zhen Zhang's avatar
Zhen Zhang committed
570
Lemma Qp_not_plus_q_ge_1 (q: Qp): ¬ ((1 + q)%Qp  1%Qp)%Qc.
571 572 573
Proof.
  intros Hle.
  apply (Qcplus_le_mono_l q 0 1) in Hle.
Zhen Zhang's avatar
Zhen Zhang committed
574
  apply Qcle_ngt in Hle. apply Hle, Qp_prf.
575
Qed.
Zhen Zhang's avatar
Zhen Zhang committed
576 577 578

Lemma Qp_ge_0 (q: Qp): (0  q)%Qc.
Proof. apply Qclt_le_weak, Qp_prf. Qed.