10 papers · 1 filter
The Hamiltonian surface of $\Aut(F_2)$
Sylvain Barré, Mikaël Pichot
The group of automorphisms of the free group on two generators is known to act geometrically, in an essentially unique way, on a 2-dimensional CAT(0) space X. We prove that X conta…
On the classification of CW complexes with prescribed links
Sylvain Barré, Mikaël Pichot
Reporting on a computer--assisted search for nonpositively curved CW complexes of intermediate rank conducted some years ago. Not intended for publication.
Sidon sequences and nonpositive curvarture
Sylvain Barré, Mikaël Pichot
A sequence of nonnegative integers is called a Sidon sequence if the sums of pairs are all different. In this paper we construct CAT(0) groups and sp…
Positive definite maps on amenable groups, II
Mikaël Pichot, Erik Séguin
We introduce an Ulam-type stability condition for positive definite maps defined on a countable group and prove that this condition characterizes amenability.
Surgery on Aut(F2)
Sylvain Barre, Mikael Pichot
We study a geometric construction of certain finite index subgroups of Aut(F2).
Pauli matrices and ring puzzles
Sylvain Barre, Mikael Pichot
We study a family of tessellations of the Euclidean plane which are obtained by local developments of algebraic equations satisfied by the Pauli matrices.