Let and be two convergent power series. Suppose that for all x in an infinite set having 0 as a point of accumulation. Then .
Define , then for an infinite set x having 0 as a point of accumulation. Now, I also know that if h(0)=0, then there exist a neighborhood centered at 0 such that h is non-constant (I actually understand the proof of that).
But how do I incorporate this idea into the proof to arrive at the conclusion that h is 0 everywhere? Thank you.