In Book 7, Prop. 1. Euclid uses repeated subtraction to prove that two numbers are relatively prime. As explained here the Greek word for repeated subtraction is "antenaresis". There isn't much information about Antenaresis online. I found this video (and the text mentioned in the video).
I have two questions. (1) Do you have more information on antenaresis and (2) What does Heath do in his commentary to the mentioned proposition?
Heath's commentary can be found on page 234 of this link:
This is the screen shot:
I understand what Euclid does but I don't understand Heath's notation.
For instance, how does Heath's notation work for a=85 and b=54?