Expensive Shoebox

The Expensive Shoebox is a story appeared in xkcd What-If #108.https://what-if.xkcd.com/108/ It concerns the most expensive way to fill a shoebox, and at the bottom, Munroe brings up the idea of writing a check, with a picture of the Shoebox Check.
In the check, it is written as 100010001000×20↑↑↑↑20×S55(1000).https://what-if.xkcd.com/imgs/a/108/check.png It may be intended to express a very large number, but it is ill-defined, because it includes an unspecified set of functions, the S functions.
== References ==
Category:Incomplete
Category:Humor