Let T be a 1-sorted structure and P , Q be subsets of the carrier of T . Let T be a 1-sorted structure and P , Q be subsets of the carrier of T . Let T be a topological structure and let P be a subset of T . P the topology of T . Let T be a topological structure and let P be a subset of T .
T P is open.
Let T be a 1-sorted structure and let F be a family of subsets of the carrier of T . Then F is a subset of T . Let T be a 1-sorted structure and let F be a family of subsets of the carrier of T . Then F is a subset of T . Let T be a 1-sorted structure and let F be a family of subsets of the carrier of T .