Isbell’s density theorem and intersection of sublocales

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 general context.  In particular, I would like to stress Isbell’s amazing density theorem, an easy but rather counterintuitive result in locale theory, and its consequence on intersections of sublocales.  Read the full post.