Tag Archives: frame

Reinhold Heckmann showed the following in a very nice paper of 2014: every countably presented locale is spatial. What makes it even nicer is that he shows how tightly this is connected with the Baire property. This also gives a … Continue reading →

Alex Simpson has a lot of slides with very interesting ideas.  One of them is what he calls the locale of random sequences.  This is a terribly clever idea that aims at solving the question “what are random sequences?”, using … Continue reading →

When I wrote my latest blog post, there were many things I thought would be useful to know about sublocales.  Those eventually turned out to be useless in that context.  However, I think they should be known, in a more … Continue reading →

In Exercise 8.4.23 of the book, I said: “Exercise 8.4.21 may give you the false impression that the O functor preserves binary products. This is wrong, although an explicit counterexample seems too complicated to study here: see Johnstone (1982, 2.14).” … Continue reading →

My goal today is to describe two elegant proofs of the fact that nuclei form a frame. There are many proofs of that. The main difficulty is that, while meets (infima) of nuclei are taken pointwise, joins (suprema) are much … Continue reading →

Last time, I promised you we would explore another way of defining sublocales.  We shall again use the naive approach that consists in imagining how we would encode subspaces of a T0 topological space X by looking at open subsets … Continue reading →

Stone duality leads naturally to the idea of locale theory.  Quickly said, the idea is that, instead of reasoning with topological spaces, we reason with frames.  The two concepts are not completely interchangeable, but the O ⊣ pt adjunction shows … Continue reading →