定义1记函数f(x)=f[1](x),f(f(x))=f[2](x),…,f(f(…f(x)…))=f[n](x),f[n](x)为f(x)的n次迭代.定义2记f(x),f[2](x),f[3](x),…,f[n](x)的定义域的交集为A,若对于任意的x∈A,存在最小的正整数n,使得f[n](x)=x,则称f(x)为n次迭代还原函数.不难证明,若f(x)为n次迭代还原函数,则 Definition 1 Note that the function f(x) = f[1](x), f(f(x)) = f[2](x), ..., f(f(...f(x)...)) = f[ n](x),f[n](x) is n iterations of f(x). Define 2 records f(x),f[2](x),f[3](x),...,f The intersection of the domain of [n](x) is A. If there is a smallest positive integer n for any x∈A such that f[n](x)=x, then f(x) is called n iterations. To restore the function, it is not difficult to prove that if f(x) is an iterative function for n iterations, then