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math.LO2021★ 1 cited
On the Pettis-Johnstone theorem for localic groups
Ruiyuan Chen
We explain how Johnstone's 1989 proof of the closed subgroup theorem for localic groups can be viewed as a point-free version of Pettis's theorem for Baire topological groups. We t…
math.CT2021
On sifted colimits in the presence of pullbacks
Ruiyuan Chen
We show that in a category with pullbacks, arbitrary sifted colimits may be constructed as filtered colimits of reflexive coequalizers. This implies that "lex sifted colimits", in…