We define a notion of flexible functor from a category X to the category of topological spaces (or other similar categories). This is a generalization of the notion of functor, where the condition of compatibility with composition is replaced by the data of homotopies, homotopies between the homotopies, and so on. When X is a site, we define a sheaf condition and show that a flexible functor (t...

1.1. Crash course in blowing up. Last time I began to talk about blowing up. Let X be a scheme, and I ⊂ OX a sheaf of ideals on X. (Technical requirement automatically satisfied in our situation: I should be a coherent sheaf, i.e. finitely generated.) Here is the “universal property” definition of blowing-up. Then the blow-up of OX along I is a morphism π : X̃ → X satisfying the following univer...

in this paper the concept of an $omega$- almost boolean ring is introduced and illistrated how a sheaf of algebras can be constructed from an $omega$- almost boolean ring over a locally boolean space.

We compare realizability models over partial combinatory algebras by embedding them into sheaf toposes. We then use the machinery of Grothendieck toposes and geometric morphisms to study the relationship between realizability models over different partial combinatory algebras. This research is part of the Logic of Types and Computation project at Carnegie Mellon University under the direction o...