Indeed. Thanks for sharing it.
I'm glad you liked it.
Here's another one.
Interesting comment. To know all there is to know in an area of maths. Knowing that we know.
“Mathematicians basically know everything there is to know about matrices. It’s one of the few subjects of math that’s thoroughly well understood,” said Jared Weinstein of Boston University.
From the Hartnett article (The ‘Useless’ Perspective That Transformed Mathematics)
That has been true for >100 years if the area is simple enough, e.g., propositional logic. (That is, logic without "for all" or "there exists," but just statements about specific things. Good enough to prove results in a finite universe, like those logic puzzles where there are five people who live in different colored houses, have different pets, etc.)
But it's hard to imagine that mathematicians literally know everything about matrices, since we know that we can't know everything even about the integers. (That's Gödel's Incompleteness Theorem.) So I think Weinstein must have been using "know everything" in the ordinary-person sense, "knows everything interesting" or "knows everything that anyone knows," etc.