实现楼道间照明灯的方便控制，一个照明灯，在楼上和楼下各有一个（闭合式）开关控制。开关的闭合并不直接决定灯的亮灭，而开关状态的改变才是决定灯亮灭的关键。即不管两个开关当前的状态如何，只要有一个开关状态发声变化，都会使照明灯在打亮或者熄灭两种状态间切换。注意，因为实际楼道中的开关为闭合式的，而板上的开关为反弹式的，所以实验时，请用手一直按着按键演示开关的闭合。(To realize the convenient control of the lights between the floors, a light, there is a (closed) switch control in the upstairs and downstairs. The closing of the switch does not directly determine the lighting of the lamp, and the change of the switch state is the key to the light of the light. That is, no matter the current state of the two switches, as long as there is a switch state, the change of voice will make the lighting switch between the two states. For example, when someone wants to go upstairs, if the headlights are extinguished, the lights will be lit after downstairs and after the switch is downloaded. And when someone upstairs again, and then click the downstairs switch (after the switch to open state), the lamp will also light up.)