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](theories/proofmode/classes.v). Most notably, many
of the tactics can be applied when the connective to be introduced or to be eliminated
appears under a later, an update modality, or in the conclusion of a
weakest precondition.
Starting and stopping the proof mode
------------------------------------
- `iStartProof PROP` : start the proof mode by turning a Coq goal into a proof
mode entailment. This tactic is performed implicitly by all proof mode tactics
described in this file, and thus should generally not be used by hand. The
optional argument `PROP` can be used to explicitly specify which BI logic
`PROP : bi` should be used. This is useful to drop down in a layered logic,
e.g. to drop down from `monPred PROP` to `PROP`.
- `iStopProof` to turn the proof mode entailment into an ordinary Coq goal
`big star of context ⊢ proof mode goal`.
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 in
either the proofmode or the Coq context. Only hypotheses in the Coq context
that are _syntactically_ of the shape `⊢ P` are recognized by this tactic
(this means that assumptions of the shape `P ⊢ Q` are not recognized).
- `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.
If the applied term has more premises than given specialization patterns, the
pattern is extended with `[] ... []`. As a consequence, all unused spatial
hypotheses move to the last premise.
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. Intuitionistic hypotheses are wrapped
into the intuitionistic 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 `pm_trm` whose conclusion is persistent.
All hypotheses can be used for proving the premises of `pm_trm`, as well as
for the resulting main goal.
- `iPoseProof pm_trm as (x1 ... xn) "ipat"` : put `pm_trm` into the context and
eliminates it. This tactic is essentially the same as `iDestruct` with the
difference that when `pm_trm` is a non-universally quantified intuitionistic
hypothesis, it will not throw the hypothesis away.
- `iAssert P with "spat" as "ipat"` : generates a new subgoal `P` and adds the
hypothesis `P` to the current goal. The specialization pattern `spat`
specifies which hypotheses will be consumed by proving `P`. The introduction
pattern `ipat` specifies how to eliminate `P`.
In case all branches of `ipat` start with a `#` (which causes `P` to be moved
to the intuitionistic context) or with an `%` (which causes `P` to be moved to
the pure Coq context), then one can use all hypotheses for proving `P` as well
as for proving the current goal.
- `iAssert P as %cpat` : assert `P` and eliminate it using the Coq introduction
pattern `cpat`. All hypotheses can be used for proving `P` as well as for
proving the current goal.
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 OFEs, and `✓ a` on discrete cameras.
- `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. Intuitionistic 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 a series of
existential quantifiers using Coq introduction patterns `x1 ... xn`, and
elimination of an object level connective using the proof mode introduction
pattern `ipat`.
In case all branches of `ipat` start with a `#` (which causes the hypothesis
to be moved to the intuitionistic context) or with an `%` (which causes the
hypothesis to be moved to the pure Coq context), then one can use all
hypotheses for proving the premises of `pm_trm`, as well as for proving the
resulting goal. Note that in this case the hypotheses still need to be
subdivided among the spatial premises.
- `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.
Separation 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 intuitionistic context.
+ `∗` : frame as much of the spatial context as possible. (N.B: this
is the unicode symbol `∗`, not the regular asterisk `*`.)
Notice that framing spatial hypotheses makes them disappear, but framing Coq
or intuitionistic hypotheses does not make them disappear.
This tactic solves the goal if everything in the conclusion has been framed.
- `iCombine "H1" "H2" as "pat"` : combines `H1 : P1` and `H2 : P2` into
`H: P1 ∗ P2`, then calls `iDestruct H as pat` on the combined hypothesis.
- `iAccu` : solves a goal that is an evar by instantiating it with a all
hypotheses from the spatial context joined together with a separating
conjunction (or `emp` in case the spatial context is empty).
Modalities
----------
- `iModIntro mod` : introduction of a modality. The type class `FromModal` is
used to specify which modalities this tactic should introduce. Instances of
that type class include: later, except 0, basic update and fancy update,
intuitionistically, persistently, affinely, plainly, absorbingly, objectively,
and subjectively. The optional argument `mod` is a term pattern (i.e., a term
with holes as underscores). If present, `iModIntro` will find a subterm
matching `mod`, and try introducing its topmost modality. For instance, if the
goal is `⎡|==> P⎤`, using `iModIntro ⎡|==> P⎤%I` or `iModIntro ⎡_⎤%I` would
introduce `⎡_⎤` and produce goal `|==> P`, while `iModIntro (|==> _)%I` would
introduce `|==>` and produce goal `⎡P⎤`.
- `iAlways` : a deprecated alias of `iModIntro`.
- `iNext n` : an alias of `iModIntro (▷^n _)`.
- `iNext` : an alias of `iModIntro (▷^_ _)`.
- `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.
Induction
---------
- `iLöb as "IH" forall (x1 ... xn) "selpat"` : 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.
- `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 intuitionistic
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 / simplification
--------------------------
- `iRewrite pm_trm` / `iRewrite pm_trm in "H"` : rewrite using an internal
equality in the proof mode goal / hypothesis `H`.
- `iRewrite -pm_trm` / `iRewrite -pm_trm in "H"` : rewrite in reverse direction
using an internal equality in the proof mode goal / hypothesis `H`.
- `iEval (tac)` / `iEval (tac) in "selpat"` : performs a tactic `tac`
on the proof mode goal / hypotheses given by the selection pattern
`selpat`. Using `%` as part of the selection pattern is unsupported.
The tactic `tac` should be a reduction or rewriting tactic like
`simpl`, `cbv`, `lazy`, `rewrite` or `setoid_rewrite`. The `iEval`
tactic is implemented by running `tac` on `?evar ⊢ P` / `P ⊢ ?evar`
where `P` is the proof goal / a hypothesis given by `selpat`. After
running `tac`, `?evar` is unified with the resulting `P`, which in
turn becomes the new proof mode goal / a hypothesis given by
`selpat`. Note that parentheses around `tac` are needed.
- `iSimpl` / `iSimpl in "selpat"` : performs `simpl` on the proof mode
goal / hypotheses given by the selection pattern `selpat`. This is a
shorthand for `iEval (simpl)`.
Iris
----
- `iInv S with "selpat" as (x1 ... xn) "ipat" "Hclose"` : where `S` is either
a namespace `N` or an identifier `H`. Open the invariant indicated by `S`.
The selection pattern `selpat` is used for any auxiliary assertions needed to
open the invariant (e.g. for cancelable or non-atomic invariants). The update
for closing the invariant is put in a hypothesis named `Hclose`.
Miscellaneous
-------------
- The tactic `done` of [std++](https://gitlab.mpi-sws.org/iris/stdpp/-/blob/master/theories/tactics.v)
(which solves "trivial" goals using `intros`, `reflexivity`, `symmetry`,
`eassumption`, `trivial`, `split`, `discriminate`, `contradiction`, etc.) is
extended so that it also, among other things:
+ performs `iAssumption`,
+ introduces `∀`, `→`, and `-∗` in the proof mode,
+ introduces pure goals `⌜ φ ⌝` using `iPureIntro` and calls `done` on `φ`, and,
+ solves other trivial proof mode goals, such as `emp`, `x ≡ x`, big operators
over the empty list/map/set/multiset.
(Note that ssreflect also has a `done` tactic. Although Iris uses ssreflect,
it overrides ssreflect's `done` tactic with std++'s.)
- 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, plainness, persistence, 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 intuitionistic context.
- `∗` : select the entire spatial context. (N.B: this
is the unicode symbol `∗`, not the regular asterisk `*`.)
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.
- `[ipat1 ipat2]` : (separating) conjunction elimination. In order to eliminate
conjunctions `P ∧ Q` in the spatial context, one of the following conditions
should hold:
+ Either the proposition `P` or `Q` should be persistent.
+ Either `ipat1` or `ipat2` should be `_`, which results in one of the
conjuncts to be thrown away.
- `(pat1 & pat2 & ... & patn)` : syntactic sugar for `[pat1 [pat2 .. patn ..]]`
to eliminate nested (separating) conjunctions.
- `[ipat1|ipat2]` : disjunction elimination.
- `[]` : false elimination.
- `%H` : move the hypothesis to the pure Coq context, and name it `H`. Support
for the `%H` introduction pattern requires an implementation of the hook
`string_to_ident`. Without an implementation of this hook, the `%H` pattern
will fail. We provide an implementation of the hook using Ltac2, which works
with Coq 8.11, and can be installed with opam; see
[iris/string-ident](https://gitlab.mpi-sws.org/iris/string-ident) for details.
- `%` : move the hypothesis to the pure Coq context (anonymously). Note that if
`%` is followed by an identifier, and not another token, a space is needed
to disambiguate from `%H` above.
- `->` and `<-` : rewrite using a pure Coq equality
- `# ipat` : move the hypothesis into the intuitionistic context. The tactic
will fail if the hypothesis is not intuitionistic. On success, the tactic will
strip any number of intuitionistic and persistence modalities. If the
hypothesis is already in the intuitionistic context, the tactic will still
strip intuitionistic and persistence modalities (it is a no-op if the
hypothesis does not contain such modalities).
- `-# ipat` : move the hypothesis from the intuitionistic context into the
spatial context. If the hypothesis is already in the spatial context, the
tactic is a no-op. If the hypothesis is not affine, an `` modality is
added to the hypothesis.
- `> 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:
- `{selpat}` : clear the hypotheses given by the selection pattern `selpat`.
Items of the selection pattern can be prefixed with `$`, which cause them to
be framed instead of cleared.
- `!%` : introduce a pure goal (and leave the proof mode).
- `!>` : introduce a modality by calling `iModIntro`.
- `!#` : introduce a modality by calling `iModIntro` (deprecated).
- `/=` : perform `simpl`.
- `//` : perform `try done` on all goals.
- `//=` : syntactic sugar for `/= //`
- `*` : 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 Hx) "!> $ [[] | #[HQ HR]] /= !>".
which results in:
x : nat
Hx : 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.
- `(H spat1 .. spatn)` : first recursively specialize the hypothesis `H` using
the specialization patterns `spat1 .. spatn`, and finally use the result of
the specialization of `H` (it should match the premise exactly). If `H` is
spatial, it will be consumed.
- `[H1 .. Hn]` and `[H1 .. Hn //]` : generate a goal for the premise with the
(spatial) hypotheses `H1 ... Hn` and all intuitionistic hypotheses. The
spatial hypotheses among `H1 ... Hn` will be consumed, and will not be
available for subsequent goals. Hypotheses prefixed with a `$` will be framed
in the goal for the premise. The pattern can be terminated with a `//`, which
causes `done` to be called to close the goal (after framing).
- `[-H1 ... Hn]` and `[-H1 ... Hn //]` : the negated forms of the above
patterns, where the goal for the premise will have all spatial premises except
`H1 .. Hn`.
- `[> H1 ... Hn]` and `[> H1 ... Hn //]` : like the above patterns, but these
patterns can only be used if the goal is a modality `M`, in which case
the goal for the premise will be wrapped in the modality `M`.
- `[> -H1 ... Hn]` and `[> -H1 ... Hn //]` : the negated forms of the above
patterns.
- `[# $H1 .. $Hn]` and `[# $H1 .. $Hn //]` : generate a goal for a persistent
premise in which all hypotheses are available. This pattern does not consume
any hypotheses; all hypotheses are available in the goal for the premise, as
well in the subsequent goal. The hypotheses `$H1 ... $Hn` will be framed in
the goal for the premise. These patterns can be terminated with a `//`, which
causes `done` to be called to close the goal (after framing).
- `[%]` and `[% //]` : generate a Coq goal for a pure premise. This pattern
does not consume any hypotheses. The pattern can be terminated with a `//`,
which causes `done` to be called to close the goal.
- `[$]` : solve the premise by framing. It will first repeatedly frame the
spatial hypotheses, and then repeatedly frame the intuitionistic hypotheses.
Spatial hypothesis that are not framed are carried over to the subsequent
goal.
- `[> $]` : like the above pattern, but this pattern can only be used if the
goal is a modality `M`, in which case the goal for the premise will be wrapped
in the modality `M` before framing.
- `[# $]` : solve the persistent premise by framing. It will first repeatedly
frame the spatial hypotheses, and then repeatedly frame the intuitionistic
hypotheses. This pattern does not consume any hypotheses.
For example, given:
H : □ P -∗ P 2 -∗ R -∗ x = 0 -∗ Q1 ∗ Q2
One 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 either a hypothesis or 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 shorthand syntaxes, too:
(H with "spat1 .. spatn")
(H $! t1 ... tn)
H
HeapLang tactics
================
If you came here looking for the `wp_` tactics, those are described in the
[HeapLang documentation](./heap_lang.md).