If there is a unique X corresponding to any Y, we can say that X and Y are in one-to-one correspondence. If there is an allusion from X to Y, it must constitute a function, where X is the independent variable and Y is the dependent variable, also known as the function of X. ..
If there is a one-to-one correspondence, the function with X as the independent variable and the function with Y as the independent variable are reciprocal functions. . . Like y = x 2, it is an allusion from x to y, but it is not a mapping from y to x, because if y = 2 x has two values that meet the conditions, it does not meet the unique definition in the mapping.
As for exponential function, he and logarithmic function are reciprocal functions. When the cardinality is greater than 1, the increasing function is less than 1, and when it is greater than 0, it is a decreasing function. The cardinal number of high school should be greater than zero, and its value range is greater than zero. It depends on the textbook. It may be a bit cumbersome to say whether the textbook is the answer given to you by experts. My answer can only give you a general understanding. . . . . I hope you can adopt.