This topic originally meant "AA looking at AA", but it is not very rigorous, because f(x+ 1)=-f(x) and f(x+2)=f(x) are not exactly the same. F(x+ 1)=-f(x) is a necessary and sufficient condition for f(x+2)=f(x). On the definition of [- 1, 1], f(x)=x2 does not satisfy f (x+65438).