Big shout-out to English mathematician John Venn, who in 1880 introduced  a very simple and visual way to demonstrate relations between sets (among other things).

Here’s the first Riordan Venn diagram (that we know of) to chart demigod appearances per Rick Riordan book series.

There’s a good chance that with the fourth installment of Trials of Apollo (The Tyrant’s Tomb) we’ll have to go back and make some adjustments (not a spoiler, really).