`(graph-vertex-exists? (G <graph>) vertex)`methodPredicate for checking if a vertex exists within graph G.

- G
- the graph to check
- vertex
- the identifier for the vertex (can be anything)

`(graph-vertex-exists? (G <graph>) vertex)`methodPredicate for checking if a vertex exists within graph G.

- G
- the graph to check
- vertex
- the identifier for the vertex (can be anything)