`(graph-vertex-add (G <graph>) vertex [#!rest attr])`method`(graph-vertex-add! (G <graph>) vertex [#!rest attr])`methodAdds a vertex with attributes

`attr`to a graph G. Raises an error if the vertex already exists within the graph.- G
- the graph you wish to add a vertex to
- vertex
- the vertex (identifier) you wish to add
- attr
- a series of keyword / value pairs that define vertex attributes