In algebraic geometry, a Schubert variety is a particular type of subvariety of a flag variety, which in turn is a parameter space for certain types of subspaces of a vector space. Schubert varieties arise in the study of intersection theory, representation theory, and several other areas of mathematics.
In algebra, particularly in the context of module theory, torsion refers to a property of elements in a module over a ring. More specifically, let \( M \) be a module over a ring \( R \). An element \( m \in M \) is said to be a torsion element if there exists a non-zero element \( r \in R \) such that \( r \cdot m = 0 \).
Wayfinder can refer to different concepts based on the context in which it's used. Here are a few possibilities: 1. **Navigation and Wayfinding**: In a general sense, a "wayfinder" can refer to tools or systems that help individuals navigate or find their way in a physical space, such as maps, signage, or GPS technology.
GPS/INS stands for Global Positioning System/Inertial Navigation System. It is a combined navigation system that integrates two different technologies to determine the position, velocity, and orientation of a moving object, such as an aircraft, vehicle, or ship. ### Global Positioning System (GPS) - **Function**: GPS uses a network of satellites that send signals to GPS receivers on the ground or in vehicles.
Kakuro is a number puzzle that is sometimes referred to as a "cross-sum" puzzle. It is similar to a crossword puzzle but uses numbers instead of words. The objective of Kakuro is to fill in the blank cells in a grid with digits from 1 to 9, such that the numbers in each group of contiguous cells sum up to the specified clues provided in the grid.
Cav1.1 refers to a type of voltage-gated calcium channel that is primarily found in skeletal muscle cells. It is a crucial component in the excitation-contraction coupling process, which translates electrical signals from the nervous system into muscle contraction. Cav1.1 is a large protein, and its full name is "calcium channel, voltage-dependent, L type, alpha 1S subunit.
Jean Baptiste Perrin by Ciro Santilli 40 Updated 2025-07-16
This seems like a cool dude. Besides a hardcore scientist, he also made many important contributions to the French education and research system.
Nabla symbol by Ciro Santilli 40 Updated 2025-07-16
Nabla is one of those: it was completely made up in modern times, and just happens to look like an inverted upper case delta to make things even more confusing!
Nabla means "harp" in Greek, which looks like the symbol.

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