If I need to find the integer valued solution to Linear programming problem using branch and bound method, but the non integer x value at the last iteration is less than 1, let's say 3/4. Then I have one constrain $x_1 \le 0$ and $x_1 \ge 1$. How do I proceed with the first case, when $x_1 \le 0$? I cannot add another constrain with auxiliary variable $x_1 + s_1 \le 0$, because all $x_i \ge 0$. Can I simply assume that $x_1 = 0$ and do the linear programming problem ignoring the $x_1$ variable?