Towards an understanding of hole superconductivity

High-Tc Copper Oxide Superconductors and Related Novel Materials Volume 255 of the series Springer Series in Materials Science pp 99-115, edited by Annette Bussmann-Holder, Hugo Keller and Antonio Bianconi, 2017. Dedicated to Prof. K. A. Müller on the Occasion of his 90th Birthday ------- arXiv:1704.07452

Abstract: From the very beginning K. Alex Müller emphasized that the materials he and George Bednorz discovered in 1986 were $hole$ superconductors. Here I would like to share with him and others what I believe to be $the$ key reason for why high $T_c$ cuprates as well as all other superconductors are hole superconductors, which I only came to understand a few months ago.