P→Q stands for natural language, "If …, then …". Obviously, when P is true and Q is false, P→Q is a false proposition, but when P is false, whether Q is true or not at this time seems impossible to judge whether P→Q is true or false, but in practice, it is reasonable to stipulate that P→Q is true. 2, then x+ 1≥3 ",obviously this proposition is true for any real number x, but when the values of x are 3, 2 and 1 respectively, the above proposition is" If 3 >; 2, then 3+ 1≥3 ","If 2 >; 2, then 2+ 1≥3 ","if1>; 2, then 1+ 1≥3 ",thus, if and only if p is true, q is false, P→Q is false, and the rest are true. Generally speaking, P→Q is if and only if p is 1 (true) and q is 0 (false), that is