Waving-hand（云手) is doing the scanning ( like radar ) with both hands (i.e. upper hand : Yang and lower hand : Yin ) from right to left and vice versa. The upper hand covers the area from the eye level down to the chest whereas the lower hand covers the area from the chest down to the belly. In other words both hands cover the entire upper part of the body to prevent being attacked. Any one hand encounters an obstacle ( by sense not merely by sight ) both hands would close up to do the twisting or locking then using 斜飞势 to throw ! The typical tai-ji mode is : neutralization (coiling) ——–〉 counter-attack. If you do not practice coiling, you could not apply tai-ji for combat. Then tai-ji is merely your morning exercise ! 近日 （七，八 月，2015）惊闻台北和北京，有凶徒持刀 伤/杀 人，故旅游者除了要记得买旅游保险外，不妨上老夫的网站，学一两招：“ 空手对白刃 ” 的太极功夫，以防万一 ，至少可以避开第一刀！
Google+Tai-ji subdues a dagger by : 顺水推舟(左刀)云手(右刀）
