public IConstr addExactly(IVecInt literals, IVec<BigInteger> coeffs, BigInteger weight)
     throws ContradictionException {
   StringBuffer out = getOut();
   assert literals.size() == coeffs.size();
   this.nbOfConstraints++;
   int n = literals.size();
   if (n > 0) {
     out.append(coeffs.get(0));
     out.append("x");
     out.append(literals.get(0));
     out.append(" ");
   }
   BigInteger coeff;
   for (int i = 1; i < n; i++) {
     coeff = coeffs.get(i);
     if (coeff.signum() > 0) {
       out.append("+ " + coeff);
     } else {
       out.append("- " + coeff.negate());
     }
     out.append("x");
     out.append(literals.get(i));
     out.append(" ");
   }
   out.append("= ");
   out.append(weight);
   out.append(" \n");
   return FAKE_CONSTR;
 }