sts.v 18.3 KB
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From prelude Require Export sets.
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From algebra Require Export cmra.
From algebra Require Import dra.
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Local Arguments valid _ _ !_ /.
Local Arguments op _ _ !_ !_ /.
Local Arguments unit _ _ !_ /.

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(** * Definition of STSs *)
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Module sts.
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Structure stsT := STS {
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  state : Type;
  token : Type;
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  prim_step : relation state;
  tok : state  set token;
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}.
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Arguments STS {_ _} _ _.
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Arguments prim_step {_} _ _.
Arguments tok {_} _.
Notation states sts := (set (state sts)).
Notation tokens sts := (set (token sts)).
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(** * Theory and definitions *)
Section sts.
Context {sts : stsT}.
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(** ** Step relations *)
Inductive step : relation (state sts * tokens sts) :=
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  | Step s1 s2 T1 T2 :
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     (* TODO: This asks for ⊥ on sets: T1 ⊥ T2 := T1 ∩ T2 ⊆ ∅. *)
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     prim_step s1 s2  tok s1  T1    tok s2  T2   
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     tok s1  T1  tok s2  T2  step (s1,T1) (s2,T2).
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Notation steps := (rtc step).
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Inductive frame_step (T : tokens sts) (s1 s2 : state sts) : Prop :=
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  | Frame_step T1 T2 :
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     T1  (tok s1  T)    step (s1,T1) (s2,T2)  frame_step T s1 s2.
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(** ** Closure under frame steps *)
Record closed (S : states sts) (T : tokens sts) : Prop := Closed {
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  closed_disjoint s : s  S  tok s  T  ;
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  closed_step s1 s2 : s1  S  frame_step T s1 s2  s2  S
}.
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Definition up (s : state sts) (T : tokens sts) : states sts :=
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  mkSet (rtc (frame_step T) s).
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Definition up_set (S : states sts) (T : tokens sts) : states sts :=
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  S = λ s, up s T.
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(** Tactic setup *)
Hint Resolve Step.
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Hint Extern 50 (equiv (A:=set _) _ _) => set_solver : sts.
Hint Extern 50 (¬equiv (A:=set _) _ _) => set_solver : sts.
Hint Extern 50 (_  _) => set_solver : sts.
Hint Extern 50 (_  _) => set_solver : sts.
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(** ** Setoids *)
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Instance framestep_mono : Proper (flip () ==> (=) ==> (=) ==> impl) frame_step.
Proof.
  intros ?? HT ?? <- ?? <-; destruct 1; econstructor;
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    eauto with sts; set_solver.
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Qed.
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Global Instance framestep_proper : Proper (() ==> (=) ==> (=) ==> iff) frame_step.
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Proof. by intros ?? [??] ??????; split; apply framestep_mono. Qed.
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Instance closed_proper' : Proper (() ==> () ==> impl) closed.
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Proof.
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  intros ?? HT ?? HS; destruct 1;
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    constructor; intros until 0; rewrite -?HS -?HT; eauto.
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Qed.
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Global Instance closed_proper : Proper (() ==> () ==> iff) closed.
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Proof. by split; apply closed_proper'. Qed.
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Global Instance up_preserving : Proper ((=) ==> flip () ==> ()) up.
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Proof.
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  intros s ? <- T T' HT ; apply elem_of_subseteq.
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  induction 1 as [|s1 s2 s3 [T1 T2]]; [constructor|].
  eapply rtc_l; [eapply Frame_step with T1 T2|]; eauto with sts.
Qed.
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Global Instance up_proper : Proper ((=) ==> () ==> ()) up.
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Proof. by intros ??? ?? [??]; split; apply up_preserving. Qed.
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Global Instance up_set_preserving : Proper (() ==> flip () ==> ()) up_set.
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Proof.
  intros S1 S2 HS T1 T2 HT. rewrite /up_set.
  f_equiv; last done. move =>s1 s2 Hs. simpl in HT. by apply up_preserving.
Qed.
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Global Instance up_set_proper : Proper (() ==> () ==> ()) up_set.
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Proof. by intros S1 S2 [??] T1 T2 [??]; split; apply up_set_preserving. Qed.
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(** ** Properties of closure under frame steps *)
Lemma closed_steps S T s1 s2 :
  closed S T  s1  S  rtc (frame_step T) s1 s2  s2  S.
Proof. induction 3; eauto using closed_step. Qed.
Lemma closed_op T1 T2 S1 S2 :
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  closed S1 T1  closed S2 T2  closed (S1  S2) (T1  T2).
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Proof.
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  intros [? Hstep1] [? Hstep2]; split; [set_solver|].
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  intros s3 s4; rewrite !elem_of_intersection; intros [??] [T3 T4 ?]; split.
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  - apply Hstep1 with s3, Frame_step with T3 T4; auto with sts.
  - apply Hstep2 with s3, Frame_step with T3 T4; auto with sts.
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Qed.
Lemma step_closed s1 s2 T1 T2 S Tf :
  step (s1,T1) (s2,T2)  closed S Tf  s1  S  T1  Tf   
  s2  S  T2  Tf    tok s2  T2  .
Proof.
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  inversion_clear 1 as [???? HR Hs1 Hs2]; intros [? Hstep]??; split_and?; auto.
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  - eapply Hstep with s1, Frame_step with T1 T2; auto with sts.
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  - set_solver -Hstep Hs1 Hs2.
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Qed.
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Lemma steps_closed s1 s2 T1 T2 S Tf :
  steps (s1,T1) (s2,T2)  closed S Tf  s1  S  T1  Tf   
  tok s1  T1    s2  S  T2  Tf    tok s2  T2  .
Proof.
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  remember (s1,T1) as sT1 eqn:HsT1; remember (s2,T2) as sT2 eqn:HsT2.
  intros Hsteps; revert s1 T1 HsT1 s2 T2 HsT2.
  induction Hsteps as [?|? [s2 T2] ? Hstep Hsteps IH];
     intros s1 T1 HsT1 s2' T2' ?????; simplify_eq; first done.
  destruct (step_closed s1 s2 T1 T2 S Tf) as (?&?&?); eauto.
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Qed.
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(** ** Properties of the closure operators *)
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Lemma elem_of_up s T : s  up s T.
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Proof. constructor. Qed.
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Lemma subseteq_up_set S T : S  up_set S T.
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Proof. intros s ?; apply elem_of_bind; eauto using elem_of_up. Qed.
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Lemma up_up_set s T : up s T  up_set {[ s ]} T.
Proof. by rewrite /up_set collection_bind_singleton. Qed.
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Lemma closed_up_set S T :
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  ( s, s  S  tok s  T  )  closed (up_set S T) T.
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Proof.
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  intros HS; unfold up_set; split.
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  - intros s; rewrite !elem_of_bind; intros (s'&Hstep&Hs').
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    specialize (HS s' Hs'); clear Hs' S.
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    induction Hstep as [s|s1 s2 s3 [T1 T2 ? Hstep] ? IH]; first done.
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    inversion_clear Hstep; apply IH; clear IH; auto with sts.
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  - intros s1 s2; rewrite !elem_of_bind; intros (s&?&?) ?; exists s.
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    split; [eapply rtc_r|]; eauto.
Qed.
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Lemma closed_up s T : tok s  T    closed (up s T) T.
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Proof.
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  intros; rewrite -(collection_bind_singleton (λ s, up s T) s).
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  apply closed_up_set; set_solver.
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Qed.
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Lemma closed_up_set_empty S : closed (up_set S ) .
Proof. eauto using closed_up_set with sts. Qed.
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Lemma closed_up_empty s : closed (up s ) .
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Proof. eauto using closed_up with sts. Qed.
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Lemma up_set_empty S T : up_set S T    S  .
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Proof. move:(subseteq_up_set S T). set_solver. Qed.
Lemma up_set_non_empty S T : S    up_set S T  .
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Proof. by move=>? /up_set_empty. Qed.
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Lemma up_non_empty s T : up s T  .
Proof. eapply non_empty_inhabited, elem_of_up. Qed.
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Lemma up_closed S T : closed S T  up_set S T  S.
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Proof.
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  intros; split; auto using subseteq_up_set; intros s.
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  unfold up_set; rewrite elem_of_bind; intros (s'&Hstep&?).
  induction Hstep; eauto using closed_step.
Qed.
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Lemma up_subseteq s T S : closed S T  s  S  sts.up s T  S.
Proof. move=> ?? s' ?. eauto using closed_steps. Qed.
Lemma up_set_subseteq S1 T S2 : closed S2 T  S1  S2  sts.up_set S1 T  S2.
Proof. move=> ?? s [s' [? ?]]. eauto using closed_steps. Qed.
End sts.

Notation steps := (rtc step).
End sts.
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Notation stsT := sts.stsT.
Notation STS := sts.STS.

(** * STSs form a disjoint RA *)
(* This module should never be imported, uses the module [sts] below. *)
Module sts_dra.
Import sts.

(* The type of bounds we can give to the state of an STS. This is the type
   that we equip with an RA structure. *)
Inductive car (sts : stsT) :=
  | auth : state sts  set (token sts)  car sts
  | frag : set (state sts)  set (token sts )  car sts.
Arguments auth {_} _ _.
Arguments frag {_} _ _.

Section sts_dra.
Context {sts : stsT}.
Infix "≼" := dra_included.
Implicit Types S : states sts.
Implicit Types T : tokens sts.

Inductive sts_equiv : Equiv (car sts) :=
  | auth_equiv s T1 T2 : T1  T2  auth s T1  auth s T2
  | frag_equiv S1 S2 T1 T2 : T1  T2  S1  S2  frag S1 T1  frag S2 T2.
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Global Existing Instance sts_equiv.
Global Instance sts_valid : Valid (car sts) := λ x,
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  match x with
  | auth s T => tok s  T  
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  | frag S' T => closed S' T  S'  
  end.
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Global Instance sts_unit : Unit (car sts) := λ x,
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  match x with
  | frag S' _ => frag (up_set S'  ) 
  | auth s _  => frag (up s ) 
  end.
Inductive sts_disjoint : Disjoint (car sts) :=
  | frag_frag_disjoint S1 S2 T1 T2 :
     S1  S2    T1  T2    frag S1 T1  frag S2 T2
  | auth_frag_disjoint s S T1 T2 :
     s  S  T1  T2    auth s T1  frag S T2
  | frag_auth_disjoint s S T1 T2 :
     s  S  T1  T2    frag S T1  auth s T2.
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Global Existing Instance sts_disjoint.
Global Instance sts_op : Op (car sts) := λ x1 x2,
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  match x1, x2 with
  | frag S1 T1, frag S2 T2 => frag (S1  S2) (T1  T2)
  | auth s T1, frag _ T2 => auth s (T1  T2)
  | frag _ T1, auth s T2 => auth s (T1  T2)
  | auth s T1, auth _ T2 => auth s (T1  T2)(* never happens *)
  end.
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Global Instance sts_minus : Minus (car sts) := λ x1 x2,
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  match x1, x2 with
  | frag S1 T1, frag S2 T2 => frag (up_set S1 (T1  T2)) (T1  T2)
  | auth s T1, frag _ T2 => auth s (T1  T2)
  | frag _ T2, auth s T1 => auth s (T1  T2) (* never happens *)
  | auth s T1, auth _ T2 => frag (up s (T1  T2)) (T1  T2)
  end.

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Hint Extern 50 (equiv (A:=set _) _ _) => set_solver : sts.
Hint Extern 50 (¬equiv (A:=set _) _ _) => set_solver : sts.
Hint Extern 50 (_  _) => set_solver : sts.
Hint Extern 50 (_  _) => set_solver : sts.
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Global Instance sts_equivalence: Equivalence (() : relation (car sts)).
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Proof.
  split.
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  - by intros []; constructor.
  - by destruct 1; constructor.
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  - destruct 1; inversion_clear 1; constructor; etrans; eauto.
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Qed.
Global Instance sts_dra : DRA (car sts).
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Proof.
  split.
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  - apply _.
  - by do 2 destruct 1; constructor; setoid_subst.
  - by destruct 1; constructor; setoid_subst.
  - by destruct 1; simpl; intros ?; setoid_subst.
  - by intros ? [|]; destruct 1; inversion_clear 1; constructor; setoid_subst.
  - by do 2 destruct 1; constructor; setoid_subst.
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  - destruct 3; simpl in *; destruct_conjs; eauto using closed_op;
      match goal with H : closed _ _ |- _ => destruct H end; set_solver.
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  - intros []; simpl; intros; destruct_conjs; split;
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      eauto using closed_up, up_non_empty, closed_up_set, up_set_empty with sts.
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  - intros ???? (z&Hy&?&Hxz); destruct Hxz; inversion Hy; clear Hy;
      setoid_subst; destruct_conjs; split_and?;
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      rewrite disjoint_union_difference //;
      eauto using up_set_non_empty, up_non_empty, closed_up, closed_disjoint; [].
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    eapply closed_up_set=> s ?; eapply closed_disjoint; eauto with sts.
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  - intros [] [] []; constructor; rewrite ?assoc; auto with sts.
  - destruct 4; inversion_clear 1; constructor; auto with sts.
  - destruct 4; inversion_clear 1; constructor; auto with sts.
  - destruct 1; constructor; auto with sts.
  - destruct 3; constructor; auto with sts.
  - intros [|S T]; constructor; auto using elem_of_up with sts.
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    assert (S  up_set S ) by eauto using subseteq_up_set.
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    set_solver.
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  - intros [|S T]; constructor; auto with sts.
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    assert (S  up_set S ); auto using subseteq_up_set with sts.
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  - intros [s T|S T]; constructor; auto with sts.
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    + rewrite (up_closed (up _ _)); auto using closed_up with sts.
    + rewrite (up_closed (up_set _ _));
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        eauto using closed_up_set with sts.
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  - intros x y ?? (z&Hy&?&Hxz); exists (unit (x  y)); split_and?.
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    + destruct Hxz;inversion_clear Hy;constructor;unfold up_set; set_solver.
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    + destruct Hxz; inversion_clear Hy; simpl; split_and?;
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        auto using closed_up_set_empty, closed_up_empty, up_non_empty; [].
      apply up_set_non_empty. set_solver.
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    + destruct Hxz; inversion_clear Hy; constructor;
        repeat match goal with
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        | |- context [ up_set ?S ?T ] =>
           unless (S  up_set S T) by done; pose proof (subseteq_up_set S T)
        | |- context [ up ?s ?T ] =>
           unless (s  up s T) by done; pose proof (elem_of_up s T)
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        end; auto with sts.
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  - intros x y ?? (z&Hy&_&Hxz); destruct Hxz; inversion_clear Hy; constructor;
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      repeat match goal with
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      | |- context [ up_set ?S ?T ] =>
         unless (S  up_set S T) by done; pose proof (subseteq_up_set S T)
      | |- context [ up ?s ?T ] =>
           unless (s  up s T) by done; pose proof (elem_of_up s T)
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      end; auto with sts.
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  - intros x y ?? (z&Hy&?&Hxz); destruct Hxz as [S1 S2 T1 T2| |];
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      inversion Hy; clear Hy; constructor; setoid_subst;
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      rewrite ?disjoint_union_difference; auto.
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    split; [|apply intersection_greatest; auto using subseteq_up_set with sts].
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    apply intersection_greatest; [auto with sts|].
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    intros s2; rewrite elem_of_intersection. destruct_conjs.
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    unfold up_set; rewrite elem_of_bind; intros (?&s1&?&?&?).
    apply closed_steps with T2 s1; auto with sts.
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Qed.
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Canonical Structure RA : cmraT := validityRA (car sts).
End sts_dra. End sts_dra.

(** * The STS Resource Algebra *)
(** Finally, the general theory of STS that should be used by users *)
Notation stsRA := (@sts_dra.RA).

Section sts_definitions.
  Context {sts : stsT}.
  Definition sts_auth (s : sts.state sts) (T : sts.tokens sts) : stsRA sts :=
    to_validity (sts_dra.auth s T).
  Definition sts_frag (S : sts.states sts) (T : sts.tokens sts) : stsRA sts :=
    to_validity (sts_dra.frag S T).
  Definition sts_frag_up (s : sts.state sts) (T : sts.tokens sts) : stsRA sts :=
    sts_frag (sts.up s T) T.
End sts_definitions.
Instance: Params (@sts_auth) 2.
Instance: Params (@sts_frag) 1.
Instance: Params (@sts_frag_up) 2.

Section stsRA.
Import sts.
Context {sts : stsT}.
Implicit Types s : state sts.
Implicit Types S : states sts.
Implicit Types T : tokens sts.

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Global Instance sts_cmra_discrete : CMRADiscrete (stsRA sts).
Proof. apply validity_cmra_discrete. Qed.

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(** Setoids *)
Global Instance sts_auth_proper s : Proper (() ==> ()) (sts_auth s).
Proof. (* this proof is horrible *)
  intros T1 T2 HT. rewrite /sts_auth.
  by eapply to_validity_proper; try apply _; constructor.
Qed.
Global Instance sts_frag_proper : Proper (() ==> () ==> ()) (@sts_frag sts).
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Proof.
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  intros S1 S2 ? T1 T2 HT; rewrite /sts_auth.
  by eapply to_validity_proper; try apply _; constructor.
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Qed.
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Global Instance sts_frag_up_proper s : Proper (() ==> ()) (sts_frag_up s).
Proof. intros T1 T2 HT. by rewrite /sts_frag_up HT. Qed.
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(** Validity *)
Lemma sts_auth_valid s T :  sts_auth s T  tok s  T  .
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Proof. done. Qed.
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Lemma sts_frag_valid S T :  sts_frag S T  closed S T  S  .
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Proof. done. Qed.
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Lemma sts_frag_up_valid s T : tok s  T     sts_frag_up s T.
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Proof. intros. by apply sts_frag_valid; auto using closed_up, up_non_empty. Qed.
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Lemma sts_auth_frag_valid_inv s S T1 T2 :
   (sts_auth s T1  sts_frag S T2)  s  S.
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Proof. by intros (?&?&Hdisj); inversion Hdisj. Qed.
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(** Op *)
Lemma sts_op_auth_frag s S T :
  s  S  closed S T  sts_auth s   sts_frag S T  sts_auth s T.
Proof.
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  intros; split; [split|constructor; set_solver]; simpl.
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  - intros (?&?&?); by apply closed_disjoint with S.
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  - intros; split_and?; last constructor; set_solver.
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Qed.
Lemma sts_op_auth_frag_up s T :
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  sts_auth s   sts_frag_up s T  sts_auth s T.
Proof.
  intros; split; [split|constructor; set_solver]; simpl.
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  - intros (?&?&?). destruct_conjs.
    apply closed_disjoint with (up s T); first done.
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    apply elem_of_up.
  - intros; split_and?.
    + set_solver+.
    + by apply closed_up.
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    + apply up_non_empty.
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    + constructor; last set_solver. apply elem_of_up.
Qed.
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Lemma sts_op_frag S1 S2 T1 T2 :
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  T1  T2    sts.closed S1 T1  sts.closed S2 T2 
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  sts_frag (S1  S2) (T1  T2)  sts_frag S1 T1  sts_frag S2 T2.
Proof.
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  intros HT HS1 HS2. rewrite /sts_frag.
  (* FIXME why does rewrite not work?? *)
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  etrans; last eapply to_validity_op; first done; [].
  move=>/=[??]. split_and!; [auto; set_solver..|].
  constructor; done.
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Qed.

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(** Frame preserving updates *)
Lemma sts_update_auth s1 s2 T1 T2 :
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  steps (s1,T1) (s2,T2)  sts_auth s1 T1 ~~> sts_auth s2 T2.
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Proof.
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  intros ?; apply validity_update.
  inversion 3 as [|? S ? Tf|]; simplify_eq/=; destruct_conjs.
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  destruct (steps_closed s1 s2 T1 T2 S Tf) as (?&?&?); auto; [].
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  repeat (done || constructor).
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Qed.
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Lemma sts_update_frag S1 S2 T1 T2 :
  closed S2 T2  S1  S2  T2  T1  sts_frag S1 T1 ~~> sts_frag S2 T2.
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Proof.
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  rewrite /sts_frag=> ? HS HT. apply validity_update.
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  inversion 3 as [|? S ? Tf|]; simplify_eq/=.
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  - split_and!; first done; first set_solver. constructor; set_solver.
  - split_and!; first done; first set_solver. constructor; set_solver.
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Qed.

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Lemma sts_update_frag_up s1 S2 T1 T2 :
  closed S2 T2  s1  S2  T2  T1  sts_frag_up s1 T1 ~~> sts_frag S2 T2.
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Proof.
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  intros ? ? HT; apply sts_update_frag; [intros; eauto using closed_steps..].
  rewrite <-HT. eapply up_subseteq; done.
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Qed.

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Lemma up_set_intersection S1 Sf Tf :
  closed Sf Tf  
  S1  Sf  S1  up_set (S1  Sf) Tf.
Proof.
  intros Hclf. apply (anti_symm ()).
  + move=>s [HS1 HSf]. split; first by apply HS1.
    by apply subseteq_up_set.
  + move=>s [HS1 Hscl]. split; first done.
    destruct Hscl as [s' [Hsup Hs']].
    eapply closed_steps; last (hnf in Hsup; eexact Hsup); first done.
    set_solver +Hs'.
Qed.

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(** Inclusion *)
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(* This is surprisingly different from to_validity_included. I am not sure
   whether this is because to_validity_included is non-canonical, or this
   one here is non-canonical - but I suspect both. *)
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Lemma sts_frag_included S1 S2 T1 T2 :
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  closed S2 T2  S2   
  (sts_frag S1 T1  sts_frag S2 T2) 
  (closed S1 T1  S1     Tf, T2  T1  Tf  T1  Tf   
                                 S2  S1  up_set S2 Tf).
Proof.
  destruct (to_validity_included (sts_dra.car sts) (sts_dra.frag S1 T1) (sts_dra.frag S2 T2)) as [Hfincl Htoincl].
  intros Hcl2 HS2ne. split.
  - intros Hincl. destruct Hfincl as ((Hcl1 & ?) & (z & EQ & Hval & Hdisj)).
    { split; last done. split; done. }
    clear Htoincl. split_and!; try done; [].
    destruct z as [sf Tf|Sf Tf].
    { exfalso. inversion_clear EQ. }
    exists Tf. inversion_clear EQ as [|? ? ? ? HT2 HS2].
    inversion_clear Hdisj as [? ? ? ? _ HTdisj | |]. split_and!; [done..|].
    rewrite HS2. apply up_set_intersection. apply Hval.
  - intros (Hcl & Hne & (Tf & HT & HTdisj & HS)). destruct Htoincl as ((Hcl' & ?) & (z & EQ)); last first.
    { exists z. exact EQ. } clear Hfincl.
    split; first (split; done). exists (sts_dra.frag (up_set S2 Tf) Tf). split_and!.
    + constructor; done.
    + simpl. split.
      * apply closed_up_set. move=>s Hs2. move:(closed_disjoint _ _ Hcl2 _ Hs2).
        set_solver +HT.
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      * by apply up_set_non_empty.
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    + constructor; last done. by rewrite -HS.
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Qed.

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Lemma sts_frag_included' S1 S2 T :
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  closed S2 T  closed S1 T  S2    S1    S2  S1  up_set S2  
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  sts_frag S1 T  sts_frag S2 T.
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Proof.
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  intros. apply sts_frag_included; split_and?; auto.
  exists ; split_and?; done || set_solver+.
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Qed.
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End stsRA.