The current nightly versions of ProB can make use of Z3 as an alternate way of solving constraints.

One can start a REPL (Read-Eval-Print-Loop) by starting probcli with the '-repl' command line option. Any predicate preceded with :z3 will be solved by Z3 considering the current machine's state. The command :z3-free can be used to solve a constraint without considering the current machine's state. The full integration of Z3 and ProB’s kernel can be enabled by setting the corresponding preference by passing

-p SMT SUPPORTED INTERPRETER TRUE

on the command line.

For Linux and Mac OS, the extension is built on our infrastructure and ships with the regular ProB download. You don't need to install Z3 on your system.

Currently, the Z3 translation is unable to cope with the following constructs:

- Generalised concatenation
- Permutation
- Iteration and Closure

When using Z3 alone, the solver will report "unsupported_type_or_expression" if it can not handle parts of a constraint.

When used together with ProB, everything Z3 can not be coped with will be handled by ProB alone automatically.

Using the repl, one can try out different examples.

First an example which can be solved by Z3 and not by ProB:

>>> X<Y & Y<X & X:INTEGER % Timeout when posting constraint: % kernel_objects:(_981727#>0) ### Warning: enumerating X : INTEGER : inf:sup ---> -1:3 Existentially Quantified Predicate over X,Y is UNKNOWN [FALSE with ** ENUMERATION WARNING **]

Using the Z3 translation it can be solved:

>>> :z3 X<Y & Y<X & X:INTEGER PREDICATE is FALSE

Now an example which can be solved by ProB’s own solver:

>>> (2|->4):{y|#x.(y=(x|->x+2))} PREDICATE is TRUE

This one cannot be solved by earlier versions of Z3 and ProB (but can now be solved in the latest nightly release):

>>> :z3 (2|->4):{y|#x.(y=(x|->x+2))} PREDICATE is UNKNOWN: solver_answered_unknown

Here an example that shows that Z3 can be used to solve constraints and obtain solutions for the open variables:

>>> :z3 {x} /\ {y} /= {} & x:1000000..20000000 & y>=0 & y<2000000 PREDICATE is TRUE Solution: x = 1000000 y = 1000000

As of version 1.10.0-beta4 you can also issue the <t>:z3-version</t> command in the REPL to obtain version information.

A paper describing the integration of ProB and Z3 has been published at iFM 2016. You can download the

- raw data from our benchmarks including the R scripts to generate the
- resulting graphs.