A universal construction in Goursat categories
An action-free characterization of weak Hopf-Galois extensions.
An outline of non-abelian cohomology in a topos : (I) The theory of bouquets and gerbes
Bicategories of partial maps
Cancellative actions
The following problem is considered: when can the action of a cancellative semigroup on a set be extended to a simply transitive action of the universal group of on a larger set.
Catégories cartésiennement fermées engendrées par des monoïdes
Categorified algebra and quantum mechanics.
Central extensions and reciprocity laws
Colimits in free categories
Commutative semigroup cohomology.
Congruences on ordered groupoids.
Constructing ordered groupoids
Construction of all homomorphisms of groupoids
Crossed modules as -categories
Crossed semimodules and Schreier internal categories in the category of monoids.
Derivations of crossed modules.
Ein Verfahren zur Ableitung der OD-Gruppoid-Familien von Brandtschen OD-Gruppoiden
Einige Bemerkungen über freie Kategorien und freie Gruppoide
Equivariant covering spaces and homotopy covering spaces.
Equivariant orientation theory.