I am trying to learn Schreier–Sims Algorithm, and looking at Mathematics and Such - Schreier–Sims algorithm.

In the 3rd line of red/yellow box in 2nd figure in the link:

I am not sure why the 2nd and 3rd arrow are there, since it should only care about '2' this time, isn't it, why are 4, 7, 9 involved?

If can recommend any good tutorial on the Schreier–Sims Algorithm, I really appreciate.