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As of version 1.3.5 ProB can make use of [http://alloy.mit.edu/kodkod/ Kodkod] as an alternate way of solving constraints. | As of version 1.3.5 ProB can make use of [http://alloy.mit.edu/kodkod/ Kodkod] as an alternate way of solving constraints. | ||

Kodkod provides a relational interface to SAT solvers and is | Kodkod provides a relational interface to SAT solvers and is the heart of the [http://alloy.mit.edu/alloy/ Alloy] tool. | ||

= How to enable Kodkod = | = How to enable Kodkod = |

As of version 1.3.5 ProB can make use of Kodkod as an alternate way of solving constraints.
Kodkod provides a relational interface to SAT solvers and is the heart of the Alloy tool.

For the command-line version you need to call prob as follows:

probcli -p KODKOD TRUE

Note: to experiment with Kodkod you may want to try out the command:

probcli -p KODKOD TRUE -repl

If in addition you want see a graphical representation of the solutions found you can use the following command and open the `out.dot` file using dotty or GraphViz:

probcli -p KODKOD TRUE -repl -evaldot ~/out.dot

For the ProB Tcl/Tk Version you should select the menu command "Enable Kodkod for Properties" in the Preferences menu.

- Types:
- Basic Types: Deferred Sets, enumerated sets, integers, booleans
- Sets of basic types
- Relations between basic types
- Higher-order types (sets of sets) are not supported

- Operators:
- Predicates: &, or, =>, <=>, not, !, #, =, /=
- Booleans: TRUE, FALSE, BOOL, bool(...)
- Sets: {..,...} {x|P}, POW, card, Cartesian product, \/, /\, -, :, /:, /<:, <<: /<<:
- Numbers: n..m, >, <, >=, <=, +, -, *, SIGMA(x).(P|x)
- Relations: <->, |->, dom, ran, id, <|, <<|, |>, |>>, ~, [...], <+, prj1, prj2, closure1
- x : S+->T, x:S-->T, ..., lambda
- currently no operations on sequences are supported

- Some limitations:
- If integers are used, a predicate can only be translated if a static analysis can estimate the interval of its possible values.
- Generally only complete predicates are translated or nothing at all, unless you set the
`KODKOD_ONLY_FULL`preference to FALSE.

Once enabled, the Kodkod translation will be used in the following circumstances:

- for solving PROPERTIES
- constraint-based assertion checking (
`-cbc_assertions`command for`probcli`or the "Check Assertions on Constants" command in the menu Verify -> Constraint-Based Checking) - constraint-based deadlock checking
- in the Eval Console in the ProB Tcl/Tk version
- for the REPL in probcli (
`probcli -p KODKOD TRUE -repl`)

By default Kodkod in ProB uses the bundled SAT4J solver.
You can switch to using **minisat** by putting a current version of `libminisat.jnilib` into ProB's `lib` directory.

Similarly, as of ProB 1.6.1-beta5 you can also use the Solver **lingeling** or **glucose** by dropping `liblingeling.dylib` or `libglucose.dylib` into ProB's lib folder (for Mac OS X; for Linux the extension will be different).
You can control the solver being used using the `KODKOD_SAT_SOLVER` preference (which has four possible values: sat4j, minisat, lingeling, glucose).

These files can be downloaded from the Kodkod download site.

If you set `KODKOD_ONLY_FULL` to `FALSE`, then the Kodkod translation can be applied to part of a predicate.
In other words, the predicate (such as the PROPERTIES) are partitioned into two parts: one that can be understood by Kodkod and the rest which will be dealt with by ProB's solver.

You can also enable symmetry by using the preference `KODKOD_SYMMETRY`.
By default, ProB will set this value to 0, i.e., symmetry is off.
This means that Kodkod can also be used within set comprehensions.
By setting the preference to a value higher than 0 you will enable symmetry within Kodkod, which may mean that not all solutions will be returned.
Setting the value too high may be counter productive; Kodkod's recommended default is 20.

Finally, you can control the number of solutions that Kodkod computes in one go using the preference `KODKOD_MAX_NR_SOLS`.
E.g., if you are interested in only one solution and `KODKOD_ONLY_FULL` is `TRUE`, then you should set this value to 1.

You can also have a look at these Wiki pages: