Use this if you are using igraph from R
| vertex {igraph} | R Documentation | 
This is a helper function that simplifies adding and deleting vertices to/from graphs.
vertex(...)
vertices(...)
| ... | See details below. | 
vertices is an alias for vertex.
When adding vertices via +, all unnamed arguments are interpreted
as vertex names of the new vertices. Named arguments are interpreted as
vertex attributes for the new vertices. 
When deleting vertices via -, all arguments of vertex (or
vertices) are concatenated via c() and passed to
delete_vertices.
A special object that can be used with together with igraph graphs and the plus and minus operators.
Other functions for manipulating graph structure: 
+.igraph(),
add_edges(),
add_vertices(),
delete_edges(),
delete_vertices(),
edge(),
igraph-minus,
path()
g <- make_(ring(10), with_vertex_(name = LETTERS[1:10])) +
  vertices('X', 'Y')
g
plot(g)