Add category Mono of injective set functions and commutative squares#266
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dschepler wants to merge 1 commit into
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Add category Mono of injective set functions and commutative squares#266dschepler wants to merge 1 commit into
dschepler wants to merge 1 commit into
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The purpose here is primarily to provide a simple example of a quasitopos which is neither an elementary topos nor thin. (Of course, a lot of the manual proofs here will go away once we can add a "Grothendieck quasitopos" property; this category is equivalent to the$\lnot\lnot$ -separated presheaves on the walking morphism category, where the $\lnot\lnot$ topology is generated by the single morphism $0 \to 1$ forming a covering sieve of $1$ .)