binomial theorem expansion quick question

Question

I'm looking at a proof online to a theorem and some of the steps to the theorem are as follows:

let $ x = y+1$ then $$x^p-1 = (y+1)^p -1 = y^p + \sum_{k=1}^{p-1} {p \choose k} y^k$$ $$\iff \frac{x^p-1}{x-1} = \frac{(y+1)^p-1}{y} = y^{p-1} + \sum_{k=1}^{p-2}{p \choose k}y^{k-1}$$ I am wondering how the $p-1$ in the sum went to $p-2$?

Answer 1

It should be $p-1$ in summation.