Discuss [Bha, §2.3-2.4]. See [Dri20, §1.3] for the notion of cones and quasi-ideals. Note that some of the remarks (e.g. Remark 2.2.15) [Bha, §2.2] may not have been covered in Lecture 1. Explain them if necessary.This is a periodic series learning seminar organized by Koji Shimizu and Shizhang Li on Banach--Colmez spaces held on each Monday at MCM110. More info can be found on the website.