User blog comment:PsiCubed2/Does anybody here know the expansion rules for BM2?/@comment-35470197-20180709144339/@comment-35470197-20180709220016

Nobody knows. Even Bashicu himself does not. You need more precise historical background, right?

First of all, Bashicu showed sentences like source codes of BASIC language, but they contain many compile-errors. So they are not definitions. You can see the original source here.

http://ja.googology.wikia.com/wiki/%E3%83%A6%E3%83%BC%E3%82%B6%E3%83%BC%E3%83%96%E3%83%AD%E3%82%B0:BashicuHyudora/BASIC%E8%A8%80%E8%AA%9E%E3%81%AB%E3%82%88%E3%82%8B%E5%B7%A8%E5%A4%A7%E6%95%B0%E3%81%AE%E3%81%BE%E3%81%A8%E3%82%81

In addition, Bashicu explained how he expands several explicit examples. For example, you can see them here.

https://www.slideshare.net/BashicuHyudora/2-77942065

In order to fix the errors on his original definitions, Fish translated them into source codes of C language. You can see them here.

http://gyafun.jp/ln/basmat.cgi?ini=s

Fish also asked Bashicu to check the behaviour of the source codes. Then Bashicu agreed that they seem to work in desired manners for him. Therefore the source codes by Fish can be considered as kind of "the definitions" of BM's.

That is why googologists can never know the precise original definition of BM's.