Why (p1 - p0) in G-step ?

[amurtadha]

First of all, we highly appreciate your efforts implementing Numbskull library, which is very helpful and practical. However, we encountered some difficulties to deeply understand some points in the code source, if you can kindly explain them, we would appreciate a lot. In the paper, the G-step is defined as follows: while, in the code source (learning.py, line 111): Where we could not understand these two points: 1- Why (p1 - p0)? 2- What “proposal” and “evidence” stand for? Thank you so much in advance. Best regards