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accepted | Symplectic K-theory |
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Nov
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comment |
The free group $F_2$ has index 12 in SL(2,$\mathbb{Z}$)
If someone is still interested in an explicit homomorphism: there is one in Example 2.5 of these notes by Keith Conrads: math.uconn.edu/~kconrad/blurbs/grouptheory/SL(2,Z).pdf |
Apr
12 |
comment |
Rock-paper-scissors…
I guess "classification" is a soft term. For me, a classification is a one-to-one correspondence to a set of data together with a dictionary that allows you to just read off the answers to many interesting questions about the original objects, or at least answer them easily. In non-trivial cases, a classification will never enable you to answer all questions easily, so one has to specify "interesting questions". In this case "what is the number of instances of a given order?" should be one and if it's the only one, then classification in the sense above reduces to enumeration. |
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Aug
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answered | Is this the CAT(0) metric on an affine building? |
Jun
30 |
comment |
Properly Discontinuous Action
Of course, if a torsion-free group acts properly discontinuously, then it acts freely. So in that case the definitions are again equivalent. |
Jun
30 |
answered | Properly Discontinuous Action |