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19 votes
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Random links and $3$-manifolds

There is no universally accepted model of random three-manifolds (or random knots/links) for that matter, however, hyperbolicity is pervasive in all known models. The most popular (but not really sati …
Igor Rivin's user avatar
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19 votes

Why is there a unique hyperbolic simplex of largest area?

Firstly, this is not something you "can easily prove by calculation": The proof (by Haagerup and Munkholm) was published in Acta. Secondly, in three dimensions, the set of ideal simplices are parame …
Igor Rivin's user avatar
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18 votes

Why are Fuchsian groups interesting?

Check out Indra's Pearls. (Mumford, Series, Wright).
Igor Rivin's user avatar
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17 votes
Accepted

Does Helly's theorem hold in the hyperbolic plane?

I don't understand your reference to the model (since the geometry of the hyperbolic plane does not depend on any model), but, in fact, the Beltrami-Klein model demonstrates that any qualitative state …
Igor Rivin's user avatar
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13 votes

How to see isometries of figure 8 knot complement

The figure 8 complement decomposes into 2 regular ideal tetrahedra (see Thurston's notes, here for example.) This gives the involution quite explicitely.
Igor Rivin's user avatar
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12 votes
Accepted

Dilogarithm, tetrahedrons, and hyperbolic space

The five term relation comes from the fact that the sum of the volumes of tetrahedra $ABCD$ and $ABCE$ equals the sum of the volumes of the three tetrahedra $ABDE, ACDE, BCDE.$ One can think of $ABCDE …
Igor Rivin's user avatar
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12 votes

Tetrahedra with prescribed face angles

The question seems a little confused, in particular since the OP is asking about dihedral angles but is calling them face angles. In any case, despite the gloom in the accepted answer, a lot is known. …
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11 votes

What sort of models did Bolyai and Lobachevsky use to demonstrate the consistency of their m...

I believe that Riemann realized that the sphere was a model for elliptic geometry (1854), while Beltrami (in 1868) introduced his model for hyperbolic space, but neither Bolyai nor Lobachevsky proved …
Igor Rivin's user avatar
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11 votes

Thurston's 24 questions: All settled?

Yes, and yes, and yes. The 1st by Perelman, the 24th by Joseph Maher.
Igor Rivin's user avatar
  • 96.4k
11 votes

Hyperbolic right-angled hexagon

The formula is: $S = \pi,$ thanks to Gauss-Bonnet.
Igor Rivin's user avatar
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10 votes

Hyperbolic Volume and Chern-Simons

The first reference known to me is Thurston, William P., Three dimensional manifolds, Kleinian groups and hyperbolic geometry, Bull. Am. Math. Soc., New Ser. 6, 357-379 (1982). ZBL0496.57005. Howev …
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10 votes
Accepted

Surface of a Ideal Tetrahedron in Hyperbolic Space H3

The answer is $4\pi.$
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9 votes

Arithmetic Fuchsian group

The answer is NO. Any four times punctured sphere admits two involutions, the quotient by which is an orbifold of the signature you describe. Similarly, you can take a punctured torus, and the quotien …
Igor Rivin's user avatar
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8 votes

The fundamental group of a closed surface without classification of surfaces?

Yes, the magic words are "The Poincare polygon theorem". For (considerably) more detail, see Fine and Rosenberger "Algebraic generalizations of discrete groups: A path to combinatorial group theory th …
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8 votes
Accepted

Can most 3 dimensional hyperbolic orbifolds with finite volume be covered by a hyperbolic ma...

Yes, this is true for all of them. Any finitely generated matrix group has a torsion-free subgroup of finite index; this is the so-called "Selberg's lemma". A canonical source is Ratcliffe's Hyperboli …
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