Differential graded Koszul duality: An introductory survey.

This is an overview on derived nonhomogeneous Koszul duality over a field, mostly based on the author's memoir L. Positselski, Memoirs of the American Math. Society 212 (2011), no. 996, vi+133. The paper is intended to serve as a pedagogical introduction and a summary of the covariant duality between DG‐algebras and curved DG‐coalgebras, as well as the triality between DG‐modules, CDG‐comodules, and CDG‐contramodules. Some personal reminiscences are included as a part of historical discussion. [ABSTRACT FROM AUTHOR]