The vertex set of a graph is simply a set of all vertices of the graph. The cardinality of the vertex set for a given graph 
is known as the vertex count
of 
.
The vertex set for a particular graph embedding of a graph 
is given in the Wolfram
Language using PropertyValue[g,
VertexCoordinates] or GraphEmbedding[g].
Vertex sets for many named graphs are available via GraphData[graph,
"VertexCoordinates"] (for the primary embedding) and GraphData[graph,
"Embeddings"] (for all available embeddings).
The vertex set 
of an abstract simplicial complex 
is the union of one-point elements of
(Munkres 1993, p. 15).
