Search `graph` for an edge whose vertexes match `edge`. This means that `vertex-1` of the edge in the graph must match `vertex-1` of `edge` and so forth. Wil signal an error of type `graph-edge-not-found-error` unless `error-if-not-found?` is nil. [?? Unused. Remove?]
| find-edge < graph-container > < graph-container-edge > |