# Math

## Why category thoery is fundamental yet hard to understand

Category theory is mathematical theory about mapping. Some call it the foundation of mathematics.

According to my understanding of math as reproducible mental object, this is not supprising. As all the brain does is doing mapping. Or in Plovian's words: conduction. Signals going from one set of neuros to another.  Understanding mapping is fundamental obviously.

Now category is billed the hardest to understand branch of mathematics, also known as "abstract nonsense".

## Yaha! A Math Game for Everyone.

Yaha! is a traditional math game popular among Chinese speaking populations. It has been historically given a varieties of names, but the essence of the game is the same: the players are given 4 playing cards, their task is to use the 4 numbers represented by the cards, use them once and only once, to get the number 24. The players are allowed to apply all four arithmetic operations: addition, subtraction, multiplication and division, as well as parenthesis as they see fit. The winner is whoever comes up with a correct solution first.

This program is a simulation of the game. It is at present form designed to be played by only one player. Remember, your goal is to form an arithmetic expression by dragging cards and operators into appropriate slots and let the result of your expression equals to 24. Got it? Click the picture below to load the game. It will start in a new window.

Nice place