ProofMode.md

Tactic overview

Many of the tactics below apply to more goals than described in this document since the behavior of these tactics can be tuned via instances of the type classes in the file proofmode/classes. Most notable, many of the tactics can be applied when the to be introduced or to be eliminated connective appears under a later, an update modality, or in the conclusion of a weakest precondition.

Applying hypotheses and lemmas

• iExact "H" : finish the goal if the conclusion matches the hypothesis H
• iAssumption : finish the goal if the conclusion matches any hypothesis
• iApply pm_trm : match the conclusion of the current goal against the conclusion of pm_trm and generates goals for the premises of pm_trm. See proof mode terms below.

Context management

• iIntros (x1 ... xn) "ipat1 ... ipatn" : introduce universal quantifiers using Coq introduction patterns x1 ... xn and implications/wands using proof mode introduction patterns ipat1 ... ipatn.
• iClear (x1 ... xn) "selpat" : clear the hypotheses given by the selection pattern selpat and the Coq level hypotheses/variables x1 ... xn.
• iRevert (x1 ... xn) "selpat" : revert the hypotheses given by the selection pattern selpat into wands, and the Coq level hypotheses/variables x1 ... xn into universal quantifiers. Persistent hypotheses are wrapped into the always modality.
• iRename "H1" into "H2" : rename the hypothesis H1 into H2.
• iSpecialize pm_trm : instantiate universal quantifiers and eliminate implications/wands of a hypothesis pm_trm. See proof mode terms below.
• iSpecialize pm_trm as # : instantiate universal quantifiers and eliminate implications/wands of a hypothesis whose conclusion is persistent. In this case, all hypotheses can be used for proving the premises, as well as for the resulting goal.
• iPoseProof pm_trm as "H" : put pm_trm into the context as a new hypothesis H.
• iAssert P with "spat" as "ipat" : create a new goal with conclusion P and put P in the context of the original goal. The specialization pattern spat specifies which hypotheses will be consumed by proving P. The introduction pattern ipat specifies how to eliminate P.
• iAssert P with "spat" as %cpat : assert P and eliminate it using the Coq introduction pattern cpat.

Introduction of logical connectives

• iPureIntro : turn a pure goal into a Coq goal. This tactic works for goals of the shape ■ φ, a ≡ b on discrete COFEs, and ✓ a on discrete CMRAs.

• iLeft : left introduction of disjunction.

• iRight : right introduction of disjunction.

• iSplit : introduction of a conjunction, or separating conjunction provided one of the operands is persistent.

• iSplitL "H1 ... Hn" : introduction of a separating conjunction. The hypotheses H1 ... Hn are used for the left conjunct, and the remaining ones for the right conjunct. Persistent hypotheses are ignored, since these do not need to be split.

• iSplitR "H0 ... Hn" : symmetric version of the above.

• iExist t1, .., tn : introduction of an existential quantifier.

Elimination of logical connectives

• iExFalso : Ex falso sequitur quod libet.
• iDestruct pm_trm as (x1 ... xn) "ipat" : elimination of existential quantifiers using Coq introduction patterns x1 ... xn and elimination of object level connectives using the proof mode introduction pattern ipat. In case all branches of ipat start with an # (moving the hypothesis to the persistent context) or % (moving the hypothesis to the pure Coq context), one can use all hypotheses for proving the premises of pm_trm, as well as for proving the resulting goal.
• iDestruct pm_trm as %cpat : elimination of a pure hypothesis using the Coq introduction pattern cpat. When using this tactic, all hypotheses can be used for proving the premises of pm_trm, as well as for proving the resulting goal.

Separating logic specific tactics

• iFrame (t1 .. tn) "selpat" : cancel the Coq terms (or Coq hypotheses) t1 ... tn and Iris hypotheses given by selpat in the goal. The constructs of the selection pattern have the following meaning:

  • % : repeatedly frame hypotheses from the Coq context.
  • # : repeatedly frame hypotheses from the persistent context.
  • ★ : frame as much of the spatial context as possible.

  Notice that framing spatial hypotheses makes them disappear, but framing Coq or persistent hypotheses does not make them disappear.

  This tactic finishes the goal in case everything in the conclusion has been framed.

• iCombine "H1" "H2" as "H" : turns H1 : P1 and H2 : P2 into H : P1 ★ P2.

Modalities

• iModIntro : introduction of a modality that is an instance of the IntoModal type class. Instances include: later, except 0, basic update and fancy update.
• iMod pm_trm as (x1 ... xn) "ipat" : eliminate a modality pm_trm that is an instance of the ElimModal type class. Instances include: later, except 0, basic update and fancy update.

The later modality

• iNext : introduce a later by stripping laters from all hypotheses.
• iLöb as "IH" forall (x1 ... xn) : perform Löb induction by generating a hypothesis IH : ▷ goal. The tactic generalizes over the Coq level variables x1 ... xn, the hypotheses given by the selection pattern selpat, and the spatial context.

Induction

• iInduction x as cpat "IH" forall (x1 ... xn) "selpat" : perform induction on the Coq term x. The Coq introduction pattern is used to name the introduced variables. The induction hypotheses are inserted into the persistent context and given fresh names prefixed IH. The tactic generalizes over the Coq level variables x1 ... xn, the hypotheses given by the selection pattern selpat, and the spatial context.

Rewriting

• iRewrite pm_trm : rewrite an equality in the conclusion.
• iRewrite pm_trm in "H" : rewrite an equality in the hypothesis H.

Iris

• iInv N as (x1 ... xn) "ipat" "Hclose" : open the invariant N, the update for closing the invariant is put in a hypothesis named Hclose.

Miscellaneous

• The tactic done is extended so that it also performs iAssumption and introduces pure connectives.
• The proof mode adds hints to the core eauto database so that eauto automatically introduces: conjunctions and disjunctions, universal and existential quantifiers, implications and wand, always, later and update modalities, and pure connectives.

Selection patterns

Selection patterns are used to select hypotheses in the tactics iRevert, iClear, iFrame, iLöb and iInduction. The proof mode supports the following selection patterns:

• H : select the hypothesis named H.
• % : select the entire pure/Coq context.
• # : select the entire persistent context.
• ★ : select the entire spatial context.

Introduction patterns

Introduction patterns are used to perform introductions and eliminations of multiple connectives on the fly. The proof mode supports the following introduction patterns:

• H : create a hypothesis named H.
• ? : create an anonymous hypothesis.
• _ : remove the hypothesis.
• $ : frame the hypothesis in the goal.
• [ipat ipat] : (separating) conjunction elimination.
• [ipat|ipat] : disjunction elimination.
• [] : false elimination.
• % : move the hypothesis to the pure Coq context (anonymously).
• # ipat : move the hypothesis to the persistent context.
• > ipat : eliminate a modality (if the goal permits).

Apart from this, there are the following introduction patterns that can only appear at the top level:

• {H1 ... Hn} : clear H1 ... Hn.
• {$H1 ... $Hn} : frame H1 ... Hn (this pattern can be mixed with the previous pattern, e.g., {$H1 H2 $H3}).
• !% : introduce a pure goal (and leave the proof mode).
• !# : introduce an always modality (given that the spatial context is empty).
• !> : introduce a modality.
• /= : perform simpl.
• * : introduce all universal quantifiers.
• ** : introduce all universal quantifiers, as well as all arrows and wands.

For example, given:

    ∀ x, x = 0 ⊢ □ (P → False ∨ □ (Q ∧ ▷ R) -★ P ★ ▷ (R ★ Q ∧ x = pred 2)).

You can write

    iIntros (x) "% !# $ [[] | #[HQ HR]] /= !>".

which results in:

    x : nat
    H : x = 0
    ______________________________________(1/1)
    "HQ" : Q
    "HR" : R
    --------------------------------------□
    R ★ Q ∧ x = 1

Specialization patterns

Since we are reasoning in a spatial logic, when eliminating a lemma or hypothesis of type P_0 -★ ... -★ P_n -★ R, one has to specify how the hypotheses are split between the premises. The proof mode supports the following specification patterns to express splitting of hypotheses:

• H : use the hypothesis H (it should match the premise exactly). If H is spatial, it will be consumed.
• [H1 ... Hn] : generate a goal with the (spatial) hypotheses H1 ... Hn and all persistent hypotheses. The spatial hypotheses among H1 ... Hn will be consumed. Hypotheses may be prefixed with a $, which results in them being framed in the generated goal.
• [-H1 ... Hn] : negated form of the above pattern.
• >[H1 ... Hn] : same as the above pattern, but can only be used if the goal is a modality, in which case the modality will be kept in the generated goal for the premise will be wrapped into the modality.
• [#] : This pattern can be used when eliminating P -★ Q with P persistent. Using this pattern, all hypotheses are available in the goal for P, as well the remaining goal.
• [%] : This pattern can be used when eliminating P -★ Q when P is pure. It will generate a Coq goal for P and does not consume any hypotheses.
• * : instantiate all top-level universal quantifiers with meta variables.

For example, given:

    H : □ P -★ P 2 -★ x = 0 -★ Q1 ∗ Q2

You can write:

    iDestruct ("H" with "[#] [H1 H2] [%]") as "[H4 H5]".

Proof mode terms

Many of the proof mode tactics (such as iDestruct, iApply, iRewrite) can take both hypotheses and lemmas, and allow one to instantiate universal quantifiers and implications/wands of these hypotheses/lemmas on the fly.

The syntax for the arguments of these tactics, called proof mode terms, is:

    (H $! t1 ... tn with "spat1 .. spatn")

Here, H can be both a hypothesis, as well as a Coq lemma whose conclusion is of the shape P ⊢ Q. In the above, t1 ... tn are arbitrary Coq terms used for instantiation of universal quantifiers, and spat1 .. spatn are specialization patterns to eliminate implications and wands.

Proof mode terms can be written down using the following short hands too:

    (H with "spat1 .. spatn")
    (H $! t1 ... tn)
    H