User blog comment:Koteitan/Purely mathematical definition of BMS/@comment-24923514-20191106231524/@comment-35470197-20191107223500

> Does (P_y)^a(x) mean "the a-th ancestor of the entry at S_x,y"?

Right.

> If so, wouldn't that mean some entries might not have any ancestors?

It is a partial recursive function, and hence the domain is not the whole set. In that case, P is just undefined.

> Finally, would it be ok if I went through the BMS article to fix any grammar mistakes and clarify a few things?

Of course, you can improve the article. If you add new information, please be certain to refer to a specific source. (People often state wrong propositions on BMS, and hence we need to be careful.)