CaDiBack BackBone Extractor

This is a tool using the CaDiCaL solver to determine the backbone of a satisfiable instance, which are those literals set to true in all models of the formula.

You need to get and compile CaDiCaL in the same directory in which you have the CaDiBack sources, i.e., before configuring and compiling it make sure to have

• ../cadical/build/libcadical.a
• ../cadical/src/cadical.hpp

Then issue ./configure && make to configure and compile it. To also test the library you also use make test (additionally or alternatively). There are further configuration options which can be listed with ./configure -h.

Usage of the tool is as follows. Given the following CNF in dimacs.cnf calling cadiback on it it will give:

$ cat dimacs.cnf
p cnf 3 4
1 2 0
1 -2 0
2 -3 0
-2 -3 0
$ cadiback -q dimacs.cnf
b 1
b -3
b 0
s SATISFIABLE

This example shows that exactly the two literals 1 and -3 are backbones and that there are models both with 2 and -2, i.e., the variable 2 is not a backbone variable. In general the tool can produce multiple b lines which are not ordered and can be interleaved with comment lines starting with c. After the extractor found all backbones it prints the b 0 line.

The backbones are printed as they are found and the output is flushed whenever a new backbone is found. This allows to use the tool in an any-time fashion. Without the -q option more comment lines are printed before, between and after the backbone section, and with higher verbosity or reporting enabled even in between 'b' lines. If the given CNF is unsatisfiable the extractor prints 's UNSATISFIABLE' instead at the end.