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It is well known that a locale is subfit iff each of its open sublocales is a join of closed ones, and fit iff each of its closed sublocales is a meet of open ones. This formulation, however, exaggerates the parallelism between the behavior of fitness and subfitness. For it can be shown that a locale is fit iff each of its sublocales is a meet of closed ones, but it is not the case that a locale is subfit iff each of its sublocales is a join of closed ones. Thus we are led to take up the very natural question of which locales have the feature that every sublocale is a join of closed sublocales. In this note we show that these are precisely the subfit locales which are scattered in the point-free sense of , and we add a variation for spatial frames.
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Richard N. Ball, Jorge Picado, Aleš Pultr, On an aspect of scatteredness in the point-free setting. Port. Math. 73 (2016), no. 2, pp. 139–152DOI 10.4171/PM/1980