User blog comment:Plain'N'Simple/Using triangular numbers to create a Conway-Arrow Level Notation (probably not what you'd expect)/@comment-35434595-20191025155632/@comment-39541634-20191027004900

"I did not know that 'the number immediately before n in the grid' can be expressed in that simple way. It is actually a novel discovery for me."

It was also a novel discovery for me. I was just playing around with it while writing my blog post, and it suddenly popped up at me. I expected finding the actual formula to be much more difficult.

(Pretty sure I'm not the first person to discover this, though)

"The role of the pair function in arithmetic is the same as the role of the Hausdorff's pair formulation (x,y) = {{x},{x,y}} in set theory."

I know the formulation, but never knew that it was Hausdorff who invented it.

This guy sure invented a lot of things (until now, I only knew his name from the term "Hausdorff Space" in topology).