I have many flaws as a pop mathematics blogger. Less depth of knowledge than I should have, for example. A tendency to start a series before I have a clear ending, so that projects will peter out rather than resolve. A-to-Z’s are different, as they have a clear direction and ending. And a frightful cultural bias, too. I’m terribly weak on mathematics outside the western tradition. Yang Hui’s Triangle, an essay I wrote about in the End 2020 A-to-Z, is a slight correction to that. I grew up learning this under a different name, that of a Western mathematician who studied the thing centuries after Yang Hui did. But then Yang Hui credited an earlier-yet mathematician, Jia Xian, for the insight. It’s difficult to get anything in mathematics named for the “correct” person.