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Mar
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awarded  Nice Answer
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Feb
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Feb
17
accepted Symplectic K-theory
Feb
17
asked Symplectic K-theory
Apr
5
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Oct
29
accepted Monoids and groups of fractions
Oct
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29
asked Monoids and groups of fractions
Nov
13
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.
Apr
11
awarded  Editor
Apr
11
revised Rock-paper-scissors…
correction
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11
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Apr
10
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Apr
10
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Apr
10
asked Rock-paper-scissors…
Aug
29
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