at 5:30 Wildberger goes through the definition of Limits https://youtu.be/K4eAyn-oK4M?t=331 https://youtu.be/K4eAyn-oK4M?t=331 If you really want to understand

at 5:30 Wildberger goes through the definition of Limits https://youtu.be/K4eAyn-oK4M?t=331 https://youtu.be/K4eAyn-oK4M?t=331 If you really want to understand these things, start here: https://www.youtube.com/playlist?list=PL5A714C94D40392AB https://www.youtube.com/playlist?list=PL5A714C94D40392AB and watch them as you work through Analysis I by Terence Tao, skipping to chapter 2 where he begins from scratch introducing the naturals, integers, etc. Wildberger even shows you how to do algebraic calculus which will help to learn the Tao book when he goes about rigorously introducing calculus defined using limits. For me that helped anyway, seeing Naturals, Ints, Rationals, and Reals constructed from scratch with all their laws/operations defined and proved by Tao then him using analysis to introduce how these tiny changes in calculus work.