Have you ever wondered why X and O are used in the popular game Tic-Tac-Toe ?
Why not use a , b for the game ?

If one looks at the english alpabets , one can fit an alphabet in 5 by 5 squares with each dark square as 1 and white square as 0, then what we have done essentially is to represent each alphabet in a 25 dimensional space.

The 26 letters

Let’s say we now plot a diagram where each alphabet can be drawn on a 2 D plan , which means reducing the dimension of the data from 25 to 2. The way it is done in mathematics is called Principal Component Analysis. The objective of principal component analysis is to reduce the dimensionality (number of variables) of the dataset but retain most of the original variability in the data. The first principal component accounts for as much of the variability in the data as possible, and each succeeding component accounts for as much of the remaining variability as possible.

Let’s look at what happens when we reduce the 25 dim data of english alphabets to 2 dim.
XoClearly we see that X and O fall in different clusters and hence can be easily diff.

Intuitively though it seems that X and O seem to be correct choices for a game, there is some math basis for their selection !