Ciro Santilli @cirosantilli 35

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What you would see the moving rod look like on a photo of a length contraction experiment, as opposed as using two locally measured separate spacetime events to measure its length.

Given the function $\psi$:the operator can be written in Planck units as:often written without function arguments as:Note how this looks just like the Laplacian in Einstein notation, since the d'Alembert operator is just a generalization of the laplace operator to Minkowski space.

Same style as MNIST, but with clothes. Designed to be much harder, and more representative of modern applications, while still retaining the low resolution of MNIST for simplicity of training.

In leanpub you write your book in a markdown variant they call Markua, marketed as "markdown for books".

TODO is there a reference implementation that runs locally for HTML output? Or the only reference implementation is closed under leanpub?

Spec: markua.com/

Some sources say that this is just the part that says that the norm of a $L^2$ function is the same as the norm of its Fourier transform.

Others say that this theorem actually says that the Fourier transform is bijective.

The comment at math.stackexchange.com/questions/446870/bijectiveness-injectiveness-and-surjectiveness-of-fourier-transformation-define/1235725#1235725 may be of interest, it says that the bijection statement is an easy consequence from the norm one, thus the confusion.

TODO does it require it to be in $L^1$ as well? Wikipedia en.wikipedia.org/w/index.php?title=Plancherel_theorem&oldid=987110841 says yes, but courses.maths.ox.ac.uk/node/view_material/53981 does not mention it.

A squeezed coherent state of light.

This is true. The level of competition in university entry exams in Asia in insane in the early 21st century compared to the West.

This is actually both good and bad. Good because it selects some very good exam passers. And bad because it selects some very good exam passers.

This makes it clear how the Lie bracket can be seen as a "measure of non-commutativity"

Because the Lie bracket has to be a bilinear map, all we need to do to specify it uniquely is to specify how it acts on every pair of some basis of the Lie algebra.

Then, together with the Baker-Campbell-Hausdorff formula and the Lie group-Lie algebra correspondence, this forms an exceptionally compact description of a Lie group.