The usual style of the gemara is to have one mishna and bring the commentary and then another mishna and commentary. Sanhedrin starts out oddly bringing the entire 1st perek of mishna on daf beis amud alef, six mishnayos. And then bringing the commentary on all of them. (The Yerushalmi does not do so.) Why did Ravina and Rav Ashi choose to arrange the 1st perek of Sanhedrin this way?

Menachem Weiman, St Louis, MO