code: private void addUnitClause(final MiniSatStyleSolver s, int a, int blocking) {
      assert this.clause.size() == 0;
      assert a != LIT_UNDEF;
      assert var(a) < s.nVars();
      this.clause.push(a);
      if (blocking != LIT_UNDEF)
        this.clause.push(blocking);
      s.addClause(this.clause, null);
      this.clause.clear();
    }
docs: Adds a unit clause to the given SAT solver.
  @param s        the sat solver
  @param a        the unit literal
  @param blocking the blocking literal