The Glueing Construction and Double Categories

We introduce Artin-Wraith glueing and locally closed inclusions in double categories. Examples include locales, toposes, topological spaces, categories, and posets. With appropriate assumptions, we show that locally closed inclusions are exponentiable, and the exponentials are constructed via Artin-Wraith glueing. Thus, we obtain a single theorem establishing the exponentiability of locally closed inclusions in these five cases.Comment: 19 pages, presented at CT201

Span, Cospan, and Other Double Categories

Given a double category D such that D_0 has pushouts, we characterize oplax/lax adjunctions between D and Cospan(D_0) such that the right adjoint is normal and restricts to the identity on D_0, where Cospan(D_0) denotes the double category on D_0 whose vertical morphisms are cospans. We show that such a pair exists if and only if D has companions, conjoints, and 1-cotabulators. The right adjoints are induced by the companions and conjoints, and the left adjoints by the 1-cotabulators. The notion of a 1-cotabulator is a common generalization of the symmetric algebra of a module and Artin-Wraith glueing of toposes, locales, and topological spaces. Along the way, we obtain a characterization of double categories with companions and conjoints as those for which the identity functor on D_0 extends to a normal lax functor from Cospan(D_0) to D.Comment: 16 page

Glueing and Orthogonality for Models of Linear Logic

We present the general theory of the method of glueing and associated technique of orthogonality for constructing categorical models of all the structure of linear logic: in particular we treat the exponentials in detail. We indicate simple applications of the methods and show that they cover familiar examples.

Motives of Deligne-Mumford Stacks

For every smooth and separated Deligne-Mumford stack $F$, we associate a motive $M(F)$ in Voevodsky's category of mixed motives with rational coefficients \mathbf{DM}^{\eff}(k,\mathbb{Q}). When $F$ is proper over a field of characteristic 0, we compare $M(F)$ with the Chow motive associated to $F$ by Toen (\cite{t}). Without the properness condition we show that $M(F)$ is a direct summand of the motive of a smooth quasi-projective variety.Comment: to appear in Advances in Mathematic