xkcd.WTF!?

Explanation ➲

In this comic, Cueball is showing a diagram titled "Venn diagram" he made about something to an unseen audience. An off-panel person informs Cueball that it is an Euler diagram, and starts to explain why, prompting Cueball to forestall the interruption and state that many things are named for Leonhard Euler (specifically Euler's constant and Euler's function apart from Euler diagram) and he just wants to call the diagram a Venn diagram to give John Venn a more equal share of the fame. His off-screen friend refuses, and mockingly states that numbers are now called "Euler letters".

This may be in response to the fact that Randall has made several comics about both Euler diagrams and Venn diagrams and has sometimes used the term Venn diagram for an Euler diagram, as in 2090: Feathered Dinosaur Venn Diagram. Maybe this was on purpose, as Cueball did here, or by mistake. In either case Randall has probably heard a lot from fans and friends when he made these comics, and thus this could be seen as a response.

A Venn diagram is a widely used diagram style that shows the logical relation between sets. It shows overlap of items in different categories (sets) by using overlapping circles (or other shapes) to stand in for categories. If an item is within a certain circle, it is in the category the circle represents. So in a Venn diagram of "animals" and "furry things", "cat" would be in the overlap between both circles, "frog" would be inside only "animals", and "kiwifruit" would only be in "furry things". "Crystals" would be outside both circles.

The title text as a Venn (and, simultaneously, an Euler) diagram

John Venn was not the first to invent the idea of drawing regions whose overlap shows the intersection of sets — that was popularized by Euler (although he may not have been the first to do it) and was known as Euler Diagrams. Venn's innovation, roughly 100 years later, was to consistently draw ALL intersections of sets, even those intersections that had no members. In a Venn diagram, all 'circles' must overlap with all other circles, even if there are no items in the overlap. This is easy enough for 2 and 3 sets, but as the number of sets increases, the diagrams can get rather complicated, as previously shown in 2122: Size Venn Diagram. These three links demonstrate the issue, in which sets can start looking very non-circular. An Euler diagram is required to depict only the non-empty combinations/sets, and therefore does not have this constraint. The diagram in the comic does not have any overlap between the left and right sections so, while it is an Euler diagram, it is not a Venn diagram.

The title text is an example of a "written" Venn diagram, with Leonhard Euler creating "most of math", both of them having created overlapping circle diagrams, and John Venn creating a cricket bowling machine. In his Wikipedia article it is stated that With his son, Venn developed a bowling machine that was able to impart spin to a cricket ball. When members of the Australian cricket team visited Cambridge in June 1909, Venn’s machine bowled Victor Trumper, one of their star batsmen. See the title text drawn as a diagram in the inserted picture.

On a side note, if Euler letters were a thing, then they would be digits. And numbers would be Euler words!