What is tested here is that the completeness of real numbers is a difficult point. You don't take the general exam, and you don't take the postgraduate entrance examination, but you may ask questions during the second interview.

We divide the point sequence {Pn(Xn, Yn)} into two series A: {xn} and B: {yn};

Then the sequences A and B are both sequences on the interval [0, 1];

According to the inference of convergence point theorem, A and B converge to A and B respectively, and the convergence subsequences are c: {xkm} and d: {ykn}.

Reuse the problem to give conditions, (it's a little troublesome here, it's not easy to say clearly)

Finally, it can be proved that f(a, b)=g(a, b), that is, the proof is finished.