The Narasimhan-Seshadri theorem is a fundamental result in the theory of vector bundles over complex curves (or Riemann surfaces). It establishes a deep connection between the geometry of vector bundles and the representation theory of groups, particularly in the context of holomorphic vector bundles on Riemann surfaces and unitary representations of the fundamental group.
The Denjoy-Wolff theorem is a result in complex analysis, particularly in the field of iterated function systems and the study of holomorphic functions. It characterizes the dynamics of holomorphic self-maps of the unit disk, specifically focusing on the behavior of iterates of such functions.
The Double Limit Theorem, often referred to in the context of limits in calculus, relates to the properties and behavior of limits involving functions of two variables.
The Unique Homomorphic Extension Theorem is a result in the field of algebra, particularly concerning rings and homomorphisms. It typically states that if you have a ring \( R \) and a subring \( S \), along with a homomorphism defined on \( S \), then there exists a unique (in the case of certain conditions) homomorphic extension of this mapping up to the whole ring \( R \).
The Whitney extension theorem is a fundamental result in the field of analysis and differential geometry, concerning the extension of functions defined on a subset of a Euclidean space to the entire space while preserving certain properties.
In computational complexity theory, a theorem typically refers to a proven statement or result about the inherent difficulty of computational problems, particularly concerning the resources required (such as time or space) for their solution.
Extensive quantities are properties of a system that depend on the amount of material or the size of the system. In other words, they are additive properties that change when the system is divided into smaller parts. Extensive quantities are proportional to the size or extent of the system. Common examples of extensive quantities include: 1. **Mass** - The total amount of matter in a system. 2. **Volume** - The amount of three-dimensional space occupied by the system.
Fusion power by Ciro Santilli 37 Updated 2025-07-16
Video 1.
Why Private Billions Are Flowing Into Fusion by Bloomberg (2022)
Source.
It is interesting that there are several different approaches to the problem. This feels a bit like quantum computing's development at the same time, increases hope that at least one will work.
Lagrange's identity is a mathematical formula that relates the sums of squares of two sets of variables. It is often stated in the context of inner product spaces or in terms of quadratic forms.
This notation is designed to be relatively easy to write. This is achieved by not drawing ultra complex ASCII art boxes of every component. It would be slightly more readable if we did that, but prioritizing the writer here.
Two wires are only joined if + is given. E.g. the following two wires are not joined:
  |
--|--
  |
but the following are:
  |
--+--
  |
Simple symmetric components:
Asymmetric components have multiple letters indicating different ports. The capital letter indicates the device, and lower case letters the ports. The wires then go into the ports:
  • D: diode
    • a: anode (where electrons can come in from)
    • c: cathode
    Sample usage in a circuit:
    --aDc--
    Can also be used vertically like aany other circuit:
    |
    a
    D
    c
    |
    We can also change the port order, the device is still the same due to capital D:
    --cDa--
    
     |
    Dac--
    
     |
    Dca--
    
       |
    --caD
  • DC DC source. Ports:
    • p: positive
    • n: negative
    E.g. a 10 V source with a 10 Ohm resistor would be:
    +---pDC_10_n---+
    |              |
    +----R_10------+
    If only one side is given, the other is assumed to be at a the ground G. We can also omit p and m in that case and assume that p is the one used, e.g. the above would be equivalent to:
    DC_10---R_10---G
    If the voltage is not given, it is assumed to be a variable voltage power supply.
  • LED: same as diode
  • I: electric current source. Ports:
  • P: potentiometer source. Ports:
    • 1: one of the sides
    • 2: the middle
    • 3: the other side
  • T: transistor. The ports are sgTd:
    • s: source
    • g: gate
    • d: gate
    Sample usage in a circuit:
    ---+
       |
    --sgTd--
    All the following are also equivalent:
       |
       g
    --sTd--
    
        |
    --Tsgd--
       |
  • V: Voltmeter. Ports:
    • p: positive
    • n: negative
    If we don't need to specify explicit positive and negative sides, we can just use:
    ---V---
    without any ports. This is notably often the case for AC circuits.
    Optionally, we can also add the sides as in:
  • ports can also be separated by double underscores from the component names to increase readability. Single underscores can also be used to increase readability of longer multi-word component names e.g.:
    RPI_PICO_W__1gp0__3gnd
                |       |
                R_2k    |
                |       |
                +-aLEDc-+
    which is the same as:
    RPI_PICO_W
    1gp0  3gnd
    |       |
    R_2k    |
    |       |
    +-aLEDc-+
    represents a circuit linking port 1 of a Raspberry Pi Pico W, which is GPIO pin 0, through a resistor and an LED, back to pin 3 of the board, which is ground.
Numbers characterizing components are put just next to each component with an underscore. When there is only one parameter, standard units are assumed, e.g.:
+-----+
|     |
C_1p  R_2k
|     |
+-----+
means:
Micro is denoted as u.
Wires can just freely come in and out of specs of a component, they are then just connected to the component, e.g.:
DC_10---R_10---G
means applying a voltage of 10 V across a 10 Ohm resistor, which would lead to a current of 1 A
If a component has more than two parameters, units are used to distinguish them when possible, e.g.:
AC_1kV_2MHz
means an AC source with:
The Nexon Computer Museum is a museum located in Seongnam, South Korea, dedicated to the history and culture of computers and gaming. Opened in 2018, it is a part of Nexon, a well-known video game company, and aims to preserve and showcase the evolution of computer technology and gaming from the 20th century to the present day.
The time-independent Schrödinger equation is a variant of the Schrödinger equation defined as:
Equation 1.
Time-independent Schrodinger equation
.
So we see that for any Schrödinger equation, which is fully defined by the Hamiltonian , there is a corresponding time-independent Schrödinger equation, which is also uniquely defined by the same Hamiltonian.
The cool thing about the Time-independent Schrödinger equation is that we can always reduce solving the full Schrödinger equation to solving this slightly simpler time-independent version, as described at: Section "Solving the Schrodinger equation with the time-independent Schrödinger equation".
Because this method is fully general, and it simplifies the initial time-dependent problem to a time independent one, it is the approach that we will always take when solving the Schrodinger equation, see e.g. quantum harmonic oscillator.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact