Some Infinities Are Bigger Than Others

The board draws a list someone swears is complete, a line drawn diagonally down it picking one digit out of each row, and a new number built from that diagonal line that turns out to match nothing already on the list. This lesson is the walk-through of why that trick always works, on any list, and what it means that it does.

Before you start. You need to be able to read a row of decimals and count on your fingers, nothing past that. The only other thing you need is patience for one trick, played twice, on two different things.