Any set H of type F in R is normally embedded in R. The converse is not true, since both on the line (and in any metric space) all sets are normally embedded.nIf R is a normal space, then in Definition 1 we can require that the set H of type F be also an open set.nA necessary and sufficient condition that an open set be normally embedded is that it be of type F . From this there follows immediately:
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