* OPB file written by RustSAT
* maximum variable: x3
* 4 clauses
* 0 cardinality constraints
* 0 pseudo-boolean constraints
1 x0 1 x1 >= 1;
1 x1 1 x2 >= 1;
-1 x3 -1 x0 >= -1;
-1 x1 -1 x2 >= -1;