while_abduce is a termination and/or safety abducer for simple while-programs. The tool and the theory behind it are presented in the [SAS14] paper.

The goal of the tool is the same with that of while_prove with the crucial difference that the precondition is not given and must be found by the tool, including the inductive definitions of all predicates used.


If you are simply looking for the latest version of while_abduce, have a look at Installation.

If you want to try out the original version underpinning the [SAS14] paper, there are two options.

  1. You can download an archive of the sources and the original benchmark suite at the SAS14 GitHub release. You will then have to build the tool according to the instructions contained within.
  2. You can download a virtual machine virtual machine from the SAS-14 website. You can run this VM using Virtual Box.

Running while_abduce.native without options will produce some help text explaining its usage.


Consider the following program (see while_prove for info on the syntax).

fields: next;
precondition: cls(x) ;
y := x;
x := x.next;
while x!=y do 
  x := x.next 

NB that the definition of cls(x) in examples/sl.defs is not consulted. The prover treats cls as an as-yet undefined predicate. Let’s try the abducer.

$ ./while_abduce.native -T -sd -P benchmarks/whl_abd/09-cyclic-list.wl 
Proved: cls^1(x) |- y := x; ...
cls { 
nil!=z * z->x' * I001^1(z, x') => cls(z)
} ; 

I001 { 
w=z => I001(z,w) | 
nil!=w * w!=z * w->y' * I001^1(z, y') => I001(z,w)

We require synthesising a definition for cls that ensures safe termination (-T) and want to see an equivalent, human-readable version (-sd, see [SAS14] for an explanation).

The abducer produces a definition for cls (and auxiliary recursive predicate I001) that amounts to a cyclic list. We can also extract the cyclic termination proof with -p as in while_prove.

Benchmarks in [SAS14]

The command

make whl_abd-tests

will run the tests discussed in the paper.

NB the Mutant tests were made available to us with permission and are not included in this image.

To obtain more information from the tests, the shell variable TST_OPTS will add command-line arguments to while_abduce.native. For example, the command

TST_OPTS=-s make whl_abd-tests

will produce statistics for each test, including runtimes. Similarly, the command

TST_OPTS=-sd make whl_abd-tests

will display the simplified inductive definitions abduced for each test. Other command-line arguments include producing LaTeX code for proofs or definitions, displaying proofs and altering the search parameters.