# "Lunar" Multiply

This problem was inspired by another jovial Numberphile video “Primes on the Moon” by Neil Sloane that you should watch first to get an idea of how this wacky “lunar arithmetic” works.

Formerly known as “dismal arithmetic”, addition and multiplication of natural numbers are redefined so that **adding** two digits means taking their **maximum**, whereas **multiplying** two digits means taking their **minimum**. For example, `2 + 7 = 7 + 2 = 7`

and `2 × 7 = 7 × 2 = 2`

. Unlike ordinary addition, there can never be a carry to the next column of digits, no matter how many individual digits are added together in that column. For numbers that consist of several digits, addition and multiplication work exactly as you learned back in grade school, except that the shifted digit columns from lunar multiplication of the individual digits are added in the same lunatic fashion. Let's look again at the example:

**Input:** Two integers (int).

**Output:** Integer (int).

**Examples:**

assert lunar_multiply(2, 3) == 2 assert lunar_multiply(8, 9) == 8 assert lunar_multiply(10, 10) == 100 assert lunar_multiply(11, 11) == 111

*The mission was taken from Python CCPS 109. It is taught for Ryerson Chang School of Continuing Education by Ilkka Kokkarinen*

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin

checkio install-plugin --ff

checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.