2 Part Technique - The Under Hook determines who is in control of the Half Guard. It is common for the opponent to use his Knee Inside to prevent the top control from being established. If you had the control and than the opponent brings his Knee Inside, you could just use your hips to Force the position. Since the top control is not established yet, knock the knee downwards and land to fold the opponent's legs. If you feel pressing down is not enough, continue the downward pressure and switch the position by forcing his legs to the other side.