Cosheaves and connectedness in formal topology

Steven Vickers

The localic definitions of cosheaves, connectedness and local connectedness are transferred from impredicative topos theory to predicative formal topology. A formal topology is locally connected (has base of connected opens) iff it has a cosheaf together with certain additional structure and properties that constrain to be the connected components cosheaf. In the inductively generated case, complete spreads (in the sense of Bunge and Funk) corresponding to cosheaves are defined as formal topologies. Maps between the complete spreads are equivalent to homomorphisms between the cosheaves. A cosheaf is the connected components cosheaf for a locally connected formal topology iff its complete spread is a homeomorphism, and in this case it is a terminal cosheaf.

Mots clés: primary; secondary; Formal topology; Predicative; Locally connected; Cosheaf; Symmetric topos; Complete spread

Domaines: Logique [math.LO]

Steven Vickers. Cosheaves and connectedness in formal topology. Annals of Pure and Applied Logic, 2011, 163 (2), pp.157. ⟨10.1016/j.apal.2011.06.024⟩. ⟨hal-00821313⟩