OK, I’m embarrassed. That is indeed what I was thinking of, but without looking it up I could only remember the first line, and for some reason I thought it was Chaucer. Which it isn’t, and couldn’t have been, being off by a century or so (which I did look up, after the answer was given.)
Okay, this one takes some setup. Content warning: math.
Two professors, Rayo and Elga, held a “largest number” duel. They took turns writing numbers on the blackboard, trying to one-up each other. Each turn had to introduce a new mathematical idea or method - no fair endlessly writing “the previous number +1”.
Elga started with 1. Rayo turned that into 1111111111111111111111111[1]. Without even lifting the chalk, Elga turned that into a number whose digits couldn’t be written out in a lifetime. What did he do?
Number of digits not exact. Just a long string of 1s. ↩︎
That’s the exact same video I got the idea from.
Sitting this one out. I know the answer.
By “without lifting the chalk” does that mean Elga did NOT write anything on the chalk board?
Did Elga erase something?
I would pursue dividing by zero, but I can’t parse how that can be suggested without lifting the chalk.
I can think of several ways to make a trivial change to what’s on the board that would result in a number too large to write in conventional notation, but all of them involve adding at least a little bit of chalk marking (and hence lifting the chalk). I can see maybe changing the number by selective erasing, as @Sigene suggested, but I can’t see any way offhand to do that to make a significantly larger number.
…Wait, never mind, I think I do know of one way.
As mathematicians’ large numbers go, though, it’s still pretty small. If it’s what I’m thinking, the second log of the number is a reasonable-sized number.
Did Elga erase a bit of the last 1 ?
Post not empty
I thought of the solution as I was scrolling down the last few posts, and yeh you’ve essentially got the answer there.
Bring it home, then.
I didn’t wanna steal pjd’s thunder but if you insist 
a 1 turns into a ! very easily with a little swipe of the eraser.
And a big swipe of the eraser turns it into 11!!!(many more factorials), which is what he did. This was not the winning move of the duel, but it was the only one I could use as a solvable riddle.
That was a quick one.
The catch is that two exclamation signs next to each other is also a mathematical symbol, and n!! is actually less than n!. Presumably, if for some God-forsaken reason you actually want to take a factorial of another factorial, you’re expected to put the first in parentheses.
From a June 27th,1945, Nancy daily comic:
In panel number one Nancy overhears two boys talking. In panel two Nancy is walking along a street and sees a lit cigar on the ground. In panel three Nancy picks up the lit cigar. In the final panel Nancy has placed the cigar in her yard, burning side up with the other end in the soil. Why does she do this?
Is she trying to grow something?
No.
Is she trying to send smoke signals?
No.
I’m not familiar with the comic so this may be inappropriate and an obvious wrong guess if it was aimed at kids, but is there some sort of gag around ‘[not] putting out’?
Does it have to do with a building component like a smokestack or chimney…or other building/industrial connection?