User few_reps

52 votes

Solving algebraic problems with topology

answered Jun 1, 2015 at 12:05

35 votes

Solving algebraic problems with topology

answered Jun 1, 2015 at 9:39

15 votes

Do unit quaternions at vertices of a regular 4-simplex, one being 1, generate a free group?

answered May 2, 2015 at 0:00

13 votes

What are your favorite instructional counterexamples?

answered Sep 28, 2015 at 7:57

9 votes

Is the fundamental group of an open arithmetic Riemann surface contained in $\Gamma(2)$

answered Oct 24, 2014 at 17:36

7 votes

Accepted

Integral orthogonal group for indefinite ternary quadratic form

answered Sep 5, 2013 at 8:24

7 votes

Accepted

"Pythagoras number" for integral matrices

answered Oct 13, 2015 at 9:43

6 votes

Does there exist a sum of two squares which is written in MORE than 4 distinct way?

answered Mar 1, 2016 at 7:07

6 votes

Accepted

Number of orbits of $\mathrm{SL}_2(\mathcal O_A)$ on $\mathbf P^1(A)$ when $A$ is a quaternion algebra

answered Nov 2, 2014 at 18:21

4 votes

Accepted

Given a positive-definite integral unimodular Gram matrix, how to find a basis of the associated lattice (over $\mathbf Q$)?

answered Nov 20, 2014 at 20:47

4 votes

Accepted

S genus of quadratic forms

answered Dec 1, 2013 at 23:24

4 votes

Accepted

Lattice automorphisms of finite order

answered Sep 16, 2013 at 23:38

4 votes

On the equivalence of a pair of binary quadratic forms

answered Apr 8, 2017 at 20:55

4 votes

Accepted

A quadratic Diophantine equation

answered Dec 16, 2015 at 12:06

3 votes

algorithm to compute the integral orthogonal group

answered Oct 3, 2013 at 14:20

3 votes

2-dimensional sublattices with all vectors having very big square (in absolute value)

answered Aug 28, 2015 at 0:22

2 votes

genus 2 Siegel theta series of 3-dimensional lattices

answered May 11, 2015 at 14:13

2 votes

Accepted

Is the spin group in a metaplectic group?

answered May 22, 2015 at 9:46

2 votes

Mass of spinor genus, positive integral quadratic forms

answered Dec 6, 2013 at 23:30

2 votes

Hurwitz integers represented as sums of two squares of Hurwitz integers

answered Dec 10, 2013 at 10:44

2 votes

Accepted

covering radius of a lattice from cyclotomic extension

answered Apr 9, 2015 at 9:29

2 votes

Integral quaternary forms and theta functions

answered Feb 21, 2016 at 19:46

1 vote

Accepted

Is the poset of affine subspaces of a vector space highly connected?

answered Feb 6, 2019 at 10:40

1 vote

Accepted

Number of vectors of fixed norm

answered Jun 25, 2016 at 9:30

1 vote

integral equivalence classes of quadratic forms

answered Jun 27, 2014 at 10:37

1 vote

Extension splitting over Sylow subgroups

answered Jun 7, 2015 at 22:29

0 votes

Accepted

Orbits of the maximal compact subgroup on the light cone for $p$-adic groups

answered Apr 21, 2015 at 20:05

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27 Answers

Solving algebraic problems with topology

Solving algebraic problems with topology

Do unit quaternions at vertices of a regular 4-simplex, one being 1, generate a free group?

What are your favorite instructional counterexamples?

Is the fundamental group of an open arithmetic Riemann surface contained in $\Gamma(2)$

Integral orthogonal group for indefinite ternary quadratic form

"Pythagoras number" for integral matrices

Does there exist a sum of two squares which is written in MORE than 4 distinct way?

Number of orbits of $\mathrm{SL}_2(\mathcal O_A)$ on $\mathbf P^1(A)$ when $A$ is a quaternion algebra

Given a positive-definite integral unimodular Gram matrix, how to find a basis of the associated lattice (over $\mathbf Q$)?

S genus of quadratic forms

Lattice automorphisms of finite order

On the equivalence of a pair of binary quadratic forms

A quadratic Diophantine equation

algorithm to compute the integral orthogonal group

2-dimensional sublattices with all vectors having very big square (in absolute value)

genus 2 Siegel theta series of 3-dimensional lattices

Is the spin group in a metaplectic group?

Mass of spinor genus, positive integral quadratic forms

Hurwitz integers represented as sums of two squares of Hurwitz integers

covering radius of a lattice from cyclotomic extension

Integral quaternary forms and theta functions

Is the poset of affine subspaces of a vector space highly connected?

Number of vectors of fixed norm

integral equivalence classes of quadratic forms

Extension splitting over Sylow subgroups

Orbits of the maximal compact subgroup on the light cone for $p$-adic groups