Assertion: set's boundary | /r/HasProperty | empty
Facets:
value: always
type: DEGREE
Source sentences:
text: If the disk is viewed as its own topological space (with the subspace topology of R2), then the boundary of the disk is empty.
text: The boundary of a set is empty if and only if the set is both closed and open (that is, a clopen set).
text: In discussing boundaries of manifolds or simplexes and their simplicial complexes, one often meets the assertion that the boundary of the boundary is always empty.
text: For example, the boundary of an open disk viewed as a manifold is empty, while its boundary in the sense of topological space is the circle surrounding the disk.