The principle of tolerance is high school, which is a knowledge point of senior one. I remember this principle was also involved in primary school. At that time, it was not that the focus was not expanded, but now it will be fully expanded in the first year of high school. In terms of inclusion principle, it is an important combinatorial mathematics method, which allows you to solve sets of any size or calculate the probability of compound events. To calculate the size of the union of several sets, first calculate the size of all single sets, then subtract the intersection of all two sets, add back the intersection of all three sets, subtract the intersection of all four sets, and so on until the intersection of all sets.