## Human activities
In any place, how can we classify human activities?
Take for example a mining town (can be a spaceship mining a rather large asteroids), we will find the following "industries"
* Industries to maintain the populace:
* Food and drinks
* Clothing
* Medical services
* Housing/construction of housing
* Policing of social order
* Education (if the town spawn more than one generation)
* Transport of human, goods and services
* Communication
* Financial services (?)
* Industries for the specific town:
* Mining
* Maintenance of mining equipment
So, is there a way to classify these industries?
and properties of the industries relative to each other,
e.g. how much populace need for policing, how it scale with population,
same with transportation, etc.
## Layer of Abstraction and Set Theory?
Programmings is about layers of abstractions.
At the bottom (not the most bottom), is logic gates.
Then it becomes instruction set at CPU levels.
Then OS/kernels.
There are other sets of abstractions, mainly coming from data-structure:
* List
* Set
* Map
* Graph
And there are domain-specific abstraction/concepts:
* Cryptography
* Encoding
* Account
* SQL
* Transactions
* Certificates, etc.
Questions: Is there a connection between set theory and these abstractions? Does these abstration represent one group in set theory?
## Sequence, Series and Wave Function
* Sequence: list of numbers, e.g.
* `1, 2, 3, 4, 5, ...`
* `1, 4, 9, 16, 25, ... `
* `1, 1/2, 1/4, 1/8, 1/16, ...`
* Series: sum of sequence, e.g.
* `1 + 2 + 3 + 4 + 5 + ...`
* `1 + 4 + 9 + 16 + 25 + ...`
* `1 + 1/2 + 1/4 + 1/8 + 1/16 + ...`
For above sequence/series, the properties are roughly "well-known", e.g. they go to infinity.
For the following series:
* `1 - 1 + 1 - 1 + 1 - 1 + 1 ...`
This series kept alternating between 1 and 0. So, there is no "definite" value of this series.
What if we represent this as "wave function", e.g. |1⟩ + |0⟩
This idea should have been explored somewhere in mathematics.
Find this mathematics.