A strange loop is a cyclic structure that goes through several levels in a hierarchical system. It arises when, by moving only upwards or downwards through the system, one finds oneself back where one started. Strange loops may involve self-reference and paradox. I heard about it in [[Gödel, Escher, Bach]] by [[Douglas Hofstadter]]. Actually, I first heard about it from [K Lars Lohn's keynote at PyCon 2016](https://www.youtube.com/watch?v=bSfe5M_zG2s) about [[Python]]. His blog is called [twobraids](https://www.twobraids.com/).