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Q: My closed question probably fits better in a different SE — do I have to ask for it to be migrated?
Time dilation, increase in mass, Lorentz contraction calcs all involve velocity of light in vacuum. But in optical media light slows down. So what of relativity calcs in media? Do we ever need to adjust the speed of light?
In combinatorics, the twelvefold way is a systematic classification of 12 related enumerative problems concerning two finite sets, which include the classical problems of counting permutations, combinations, multisets, and partitions either of a set or of a number. The idea of the classification is credited to Gian-Carlo Rota, and the name was suggested by Joel Spencer.
== Overview ==
Let N and X be finite sets. Let
n
=
|
N
|
{\displaystyle n=|N|}
and
x...
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Consider a $d=0+1$ theory of fermions, i.e., fermionic QM:
$$
L=i\psi\partial_t\psi-V(\psi)
$$
The Hamiltonian is just $H=V$.
What is the definition of a symmetry here? I can construct transformations that commute with $V$ but not with the kinetic term, so they leave $H$ invariant but not $L$. Ar...
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There is an existing discussion/request for a system to tag or otherwise indicate level of questions:
Can we have a level-of-question tag please?
Differentiate research-level questions?
The idea is that people answering or searching could use this to filter questions. The indicator could for exam...
