We provide a framework for extensions of Lie algebroids, including non-abelian extensions and Lie algebroids over different bases. Our approach involves Ehresmann connections, which allows straight generalizations of classical constructions. We exhibit a filtration in cohomology and explain the associated spectral sequence. We also give a description of the groupoid integrating an extension in ...

We show how to construct a graded locally compact Hausdorff \'etale groupoid from C*-algebra carrying coaction of discrete group, together with suitable abelian subalgebra. call this the extended Weyl groupoid. When is trivial and subalgebra Cartan, our agrees Renault's prove that if G second-countable grading interior trivially isotropy torsion free, then its reduced isomorphic as G. In partic...

In this note we describe a seemingly new approach to the complex representation theory of the wreath product G o Sd where G is a finite abelian group. The approach is motivated by an appropriate version of Schur-Weyl duality. We construct a combinatorially defined groupoid in which all endomorphism algebras are direct products of symmetric groups and prove that the groupoid algebra is isomorphi...

We prove a spectral theorem for bimodules in the context of graph C∗-algebras. A bimodule over a suitable abelian algebra is determined by its spectrum (i.e., its groupoid partial order) iff it is generated by the Cuntz– Krieger partial isometries which it contains iff it is invariant under the gauge automorphisms. We study 1-cocycles on the Cuntz–Krieger groupoid associated with a graph C∗-alg...

We show that the theory of hyperrings, due to M. Krasner, supplies a perfect framework to understand the algebraic structure of the adèle class space HK = AK/K of a global field K. After promoting F1 to a hyperfield K, we prove that a hyperring of the form R/G (where R is a ring and G ⊂ R× is a subgroup of its multiplicative group) is a hyperring extension of K if and only if G ∪ {0} is a subfi...

We exhibit a finite basis M for a certain variety V of medial groupoids. The setM consists of the medial law (xy)(zt) = (xz)(yt) and five other identities involving four variables. The variety V is generated by the four groupoids ±x± y on the integers. Since V is a very natural variety, proving it to be finitely based should be of interest. In an earlier paper, we made a conjecture which implie...

We present a development of the theory of higher groups, including infinity groups and connective spectra, in homotopy type theory. An infinity group is simply the loops in a pointed, connected type, where the group structure comes from the structure inherent in the identity types of Martin-Löf type theory. We investigate ordinary groups from this viewpoint, as well as higher dimensional groups...

This paper continues the study of generalized amalgamation properties begun in [1], [2], [3], [5], and [6]. Part of the paper provides a finer analysis of the groupoids that arise from failure of 3-uniqueness in a stable theory. We show that such groupoids must be abelian and we link the binding group of the groupoids to a certain automorphism group of the monster model, showing that the group ...

The goal of this lecture is to explain in detail the statement that a Picard groupoid is “the same thing as” an Ω-spectrum E with πi(E) = 0 for i 6= 0, 1. Along the way we introduce the notion of a (very special) Γ-space, which provides one of the possible ways of formalising the concept of an “abelian group structure defined up to all the higher homotopies”, and we present an approach to K-the...