ELI5: Explain Like I'm 5

Banach–Mazur game

Okay, so the Banach-Mazur game is a fun game you can play with your friend that involves taking turns to create shapes out of a certain type of material. The goal of the game is for each player to create a shape that is as close as possible to the shape the other player created, using the same amount of material.

Imagine you have a bunch of play dough or clay that you can shape into any form you like. You and your friend start by choosing how much material you want to use for the game, say a certain amount of play dough each. You can use any tool you want to shape the play dough, like scissors, a rolling pin, or your hands.

The game starts with one player creating a shape out of their play dough and placing it on the table. Then, the other player tries to create a shape that is as close as possible to the shape the first player made, using only their own play dough.

The catch is that neither player can see the other player's shape while they are creating their own - they have to guess what the shape might look like based on what they can see from their own side of the table. This means that the shapes might look quite different from each other, but if the players used the same amount of material and took the same amount of time to create them, they will be considered equally good.

The Banach-Mazur game is like this play dough game, but instead of using play dough, we use mathematical objects called "normed vector spaces". These are like imaginary play dough that we can shape and manipulate using mathematical rules.

Normed vector spaces are used in mathematics to describe things like distances and proportions between objects, and the Banach-Mazur game is a way of exploring ideas about how these spaces work. By playing the game, mathematicians can learn more about how these spaces behave and how to measure them accurately.

So, that's the Banach-Mazur game - a fun way to play with mathematical shapes and explore the fascinating world of normed vector spaces. Have fun!