8 papers
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.
Positive definite maps on amenable groups
Mikaël Pichot, Erik Séguin
We describe conditions that characterize amenability for groups in terms of positive definite functions valued in a von Neumann algebra.
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.
A virtual geometric action of a braid group
Sylvain Barre, Mikael Pichot
We study a geometric action on a CAT(0) space of a finite index subgroup of the quotient group of the braid group on 4 strands by its center.
Isomorphisms and parity of complexes of rank 7/4
Sylvain Barre, Mikael Pichot
We study the isomorphism types of simply connected complexes of rank 7/4 using a local invariant called the parity. We show that the parity can be computed explicitly in certain co…