10th Grade · Ages 15–16
The Diagonal Year
Fifteen is old enough for the argument that broke mathematics open — and young enough to be annoyed that nobody mentioned it sooner.
- 1 Hard Thing
- 5 days · 125 minutes
- 3 unmarkable questions
Ready?
10th Grade · Count the Infinite
Fifteen is old enough for the argument that broke mathematics open — and young enough to be annoyed that nobody mentioned it sooner.
Full screen — no distractions
Where this goes
The ladder
The same idea, three times, roughly a year apart. This is what depth looks like from the outside.
This year
The diagonal, drawn by hand.
Next year
The halting problem — the same proof wearing different clothes.
The year after
Gödel's incompleteness: the third outing of the same trick, and the one that ended a century of certainty.
What lives on the desk this year
- Graph paper for the grid
- A reading list you wrote yourself
- One paper you are trying to read that is too hard for you
- A person a decade older who takes you seriously
- A five-year question
The rest of 10th Grade
One hard thing a day is the sharp end. It sits on top of an ordinary year.
Last updated: September 2026