todo.txt

Action Items:
=============
- Respond to Tom Rodeheffer's 24 September 2013 bug report about
  USE/HIDE DEF.
  Damen will Look at the code and see how much work it would be to
  implement the missing features.

* Investigate Dan's report of a self-test failing when installing
  the latest version.  (2 November 2013)
  Can't be duplicated. DONE

- Bug reported by Stephan on fingerprinting removing domain
  assumptions.  Damien investigating.

- Put TLAPS bugs on CodePlex
  Tomer doing it?

- Add to the documentation a real explanation of how one changes
  the default SMT solver--e.g., that you have to do something different
  when using Windows with Cygwin.  Also note that with the Toolbox, the
  change should usually be made as a Preference.
  Changes made, review in progress.

- Fix TLA and TLAPS web pages.
  Jael will identify problems, Tomer will fix Inria site and Leslie will
  fix Microsoft site.

- Fix Toolbox to remove pointers to tlaplus.net.
  About TLA+ Toolbox.


Proof Manager
=============

v0.3.x (development branch)
---------------------------
* Improve error messages for illegal uses of HAVE, TAKE, etc.
  DONE

- Handle input in tla2sany dump format. Add option (set by default) to
  expect input in this format.

- Handle non-Leibniz user-defined operators.

- Named Subexpressions

- Module Instantiation (implemented)

- Implement BY/USE/HIDE MODULE Foo
  (so it importd unnamed theorems from the module as well as named ones)
  and BY/USE/HIDE DEFS MODULE Foo.
  The requires deciding what USE Foo means if Foo is the
  current module.  In particular, does a global USE mark as used
  only the theorems encountered so far or all later theorems as well.

==================================================================

Isabelle / Zenon
----------------
- Reasoning about the operators defined in the following modules:
  - Integers
  - Sequences
  - FiniteSets
  - TLC: @@ and :>
    => Isabelle supports these, but I doubt that the PM does (SM 2013-11-07)
  - Reals

- Temporal reasoning

==================================================================

Misc
-------------
- Change documentation and PM so definition in named
  THEOREM/ASSUMPTION is by default USEd.

  - done on PM side

- There is now no way to use an unnamed theorem or assumption.  This
  should be fixed.
  It will be handled by the USE/BY MODULE Foo construct, which
  will use the unnamed as well as the named theoresm of Foo.

- PM/Zenon/Isabelle does not yet handle expressions
      {e : x_1 \in S_1, ... , x_n \in S_n}
  for n > 1.

====================================================================
                EVERYTHING THAT'S NOT YET DONE
                ------------------------------

General remark about the PM: there is a difference between what the PM
can translate if there were something to translate to, and what the PM
cannot translate. The former I'm marking as "awaiting backend support"
or "need to figure out canonical pragmas", while the latter as "in
progress" or "planned". The difference between the latter two is that
I had not begun working on any of the planned items. -- Kaustuv


LOGIC
- Quantifiers such as \A <<x, y>> and  \E <<x, y>> \in S \X T
PM: waiting for backend support
Zenon: 2 weeks after Isabelle encodes it
Isabelle: Isabelle supports quantification of the form \E <<x,y,z,u,v>> \in S for
  variable tuples up to length 5 (and S can in particular be a product) but the
  PM probably doesn't use this, so it has never been tested. It looks harder to
  extend the grammar for tuples of arbitrary length, but if it's important I can
  look into it.

- CHOOSE
PM: need to figure out canonical pragmas
Zenon: CHOOSE is supported (2009-07-03, rev 11743)
Isabelle: CHOOSE is fully supported, but not automated

  The two following theorems are useful for reasoning about CHOOSE
  expressions "manually". They correspond to the Isabelle rules
  chooseI2 and bChooseI2.

THEOREM ChooseIntro ==
   ASSUME NEW P(_), NEW Q(_),
          \E x: P(x),
          \A x: P(x) => Q(x)
   PROVE  Q(CHOOSE x: P(x))
OBVIOUS


THEOREM BoundedChooseIntro ==
   ASSUME NEW P(_), NEW Q(_), NEW S,
          \E x \in S : P(x),
          \A x \in S : P(x) => Q(x)
   PROVE  Q(CHOOSE x \in S : P(x))
OBVIOUS

-------------------------------------------------------
SETS
- expressions of the form {e : x_1 \in S_1, ...  , x_n \in S_n}
  for n > 1
PM: waiting for backend support
Zenon: 1 week after Isabelle encodes it
Isabelle: to be done

-------------------------------------------------------
FUNCTIONS
-Function definitions
PM: waiting for backend support for functions of multiple arguments
Zenon: single arguments work
Isabelle: single arguments work

-Recursive function definitions
PM: turns into the equivalent CHOOSE form now. In the long run the
    backends will have to provide some facility for recursive functions.
Zenon:
Isabelle:

-Functions of multiple arguments.
PM: waiting for backend support
Zenon: waiting for Isabelle, not sure how much work there will be
Isabelle: to be done

-Complex EXCEPT expressions such as:

    [f EXCEPT ![u] = x, ![v] = y]  (* multiple exceptions *)
    [f EXCEPT ![u][v] = x]         (* multiple arguments to exception *)
    [f EXCEPT ![u] = @ + 1]        (* @ expressions *)

PM: simplifies into basic EXCEPT forms using rules on
    page 304 of TLA+ book. This is suboptimal in the long
    run because this simplification is not checked by
    Isabelle/TLA+.
    2013-11-07 (SM): I believe EXCEPT forms are now fully supported, please check
    and either delete item or explain what should be done.
Zenon: nothing to do (depend on PM)?
Isabelle: nothing to do (depend on PM)?

-------------------------------------------------------
NUMBERS

-Real Numbers
  Currently not supported by any backend. Could easily be added to SMT.
PM: waiting for backend support
Zenon: not supported
Isabelle: not supported
-------------------------------------------------------
MISCELLANEOUS CONSTRUCTS

- INSTANCE
PM: (implemented a version)
Zenon & Isabelle: no plans (rely on PM)

- RECURSIVE operator definitions
    Not supported in initial release.
-------------------------------------------------------
PROOF CONSTRUCTS

-  Operators like NEW P(_) in an ASSUME/PROVE
PM:
  The following ALREADY works fine.

     THEOREM ASSUME NEW P(_), NEW Q(_), NEW R,
                    \A x : P(x) => R,
                    \A x : Q(x) => R
             PROVE \A x : P(x) \/ Q(x) => R
     OBVIOUS

  What does not work and CANNOT work in a first order system is a
  theorem such as:

     THEOREM ASSUME NEW x,
                    ASSUME NEW P(_) PROVE P(x)
             PROVE x # x
     OBVIOUS

  2013-11-07 (SM): This actually works (proved by Isabelle). I believe we can
                   delete this item.
Zenon: This will need a major rework to add higher-order
Isabelle:  Nothing to do (any free symbols are implicitly universally
  quantified)

- Using level of defined operators.  For example, this
  does not work

        f == 42
        THEOREM f' = f
        OBVIOUS

PM: Currently works when definition of f is expanded. Whether this should be required or
    not is an issue for the action front end.
Zenon: rely on PM
Isabelle: rely on PM

- STATE, ACTION, TEMPORAL declarations in ASSUME/PROVEs
PM: To be done by appropriate front ends.
Zenon: rely on PM?
Isabelle: Extension to temporal logic will handle temporal formulas.

- USE/HIDE MODULE
PM:       in progress
Zenon:    Nothing to do?
Isabelle: Nothing to do (rely on PM)
-------------------------------------------------------
TEMPORAL OPERATORS
  To be handled by specific front end(s)
-------------------------------------------------------
STANDARD MODULES

MODULE Naturals
MODULE Integers

- Integer arithmetic is implemented in particular in the SMT front end, with full
  support for linear integer arithmetic.

- * and ^ are available in Isabelle and SMT but with little automation.

- \div and % are available in Isabelle and SMT but with little automation.

- .. is fully supported by SMT. To be done in Isabelle.

MODULE Sequences
- All operators (except SelectSeq and SubSeq?) are defined in the Isabelle and SMT
  backends. Theorems are available through MODULE SequencesTheorems.

MODULE FiniteSets

- Theorems are available through MODULE FiniteSetTheorems.

MODULE TLC
- :>, @@
PM: waiting for Zenon
Zenon: need to add rules
Isabelle: fully supported

- Permutations, SortSeq
To be supported through a standard module?


MODULE Reals
- Not supported by any backend.


MODULE Bags
- Initial draft of standard module for theorems, to be consolidated.

MODULE RealTime
- No support.

-------------------------------------------------------
ERRORS
  Currently, error reporting is pretty bad.
PM: in progress
Zenon: not sure how and what to improve
Isabelle: Nothing much can be done?
 -> For auto and simp it would be useful to display the simplified
    goal to the user when these methods terminate without solving the
    goal. NB: "by auto" will just fail if the proof doesn't succeed,
    but if one writes "apply auto", Isabelle prints the simplified goal
    ("done" then finishes the proof if there is nothing left to prove).

       I've tried this before. In non-interactive mode (e.g., with
       use_thy, as we currently use), apply auto doesn't print
       anything. -- Kaustuv