Dear category theorists, in a recent note, David Roberts makes a curious point about the unsettled debate between Mochizuki and Scholze-Stix, who, as you will have heard, do not agree either on Mochizuki's proposed proof of the abc-conjecture, nor on Scholze-Stix's proposed rebuttal of that proof. David points out that the sticking points, at least of that latest exchange, are not in hard number theory but... in basic category theory. See his announcement here thehighergeometer.wordpress.com/2018/09/28/on-mochiukis-report-on-discussions/ with a link to the 7-page note here: thehighergeometer.files.wordpress.com/2018/09/mochizuki_final1.pdf This walks the reader through some examples in Mochizuki's arguments, pointing out how basic category theory seems to be the toolboox missing here. This might be an interesting point for interested category theorists to explore further. If David is right about his analysis of Mochizuki's latest "Report", then the whole of his series of articles in the IUTT-series would still be waiting for somebody to go through from a category theorist's perspective. [For admin and other information see: http://www.mta.ca/~cat-dist/ ]