Continuous cohesion over sets

Matias Menni

A pre-cohesive geometric morphism $p:\cal E \rightarrow \cal S$ satisfies Continuity if the canonical $p_! (X^{p^* S}) \rightarrow (p_! X)^S$ is an iso for every $X$ in $\cal E$ and $S$ in $\cal S$. We show that if $\cal S = Set$ and $\cal E$ is a presheaf topos then, $p$ satisfies Continuity if and only if it is a quality type. Our proof of this characterization rests on a related result showing that Continuity and Sufficient Cohesion are incompatible for presheaf toposes. This incompatibility raises the question whether Continuity and Sufficient Cohesion are ever compatible for Grothendieck toposes. We show that the answer is positive by building some examples.

Keywords: topos, Axiomatic Cohesion

2010 MSC: 18B25, 03G30

Theory and Applications of Categories, Vol. 29, 2014, No. 20, pp 542-568.

Published 2014-09-17.

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