You may be familiar with the technique to cast out 9s, which is used for some mathematical-based magic tricks (see, for example, Martin Gardner, Harry Lorayne, or Arthur Benjamin). Federico Ludueña shares his thoughts and extensions to this method, and in particular, he expands the method to casting out 10s, which is faster.
1st edition 2026, PDF 10 pages.
word count: 1224 which is equivalent to 4 standard pages of text
