-(defmethod find-edge-between-vertexes ((graph basic-graph) (value-1 t) (value-2 t)
- &key (error-if-not-found? t))
- (let ((v1 (find-vertex graph value-1 error-if-not-found?))
- (v2 (find-vertex graph value-2 error-if-not-found?)))
- (aif (and v1 v2 (find-edge-between-vertexes graph v1 v2))
- it
- (when error-if-not-found?
- (error 'graph-edge-not-found-error :vertex-1 v1 :vertex-2 v2)))))
+(defmethod find-edge-between-vertexes
+ ((graph basic-graph) (value-1 t) (value-2 t)
+ &key (error-if-not-found? t))
+ (let* ((v1 (find-vertex graph value-1 error-if-not-found?))
+ (v2 (find-vertex graph value-2 error-if-not-found?)))
+ (or (and v1 v2 (find-edge-between-vertexes graph v1 v2)))
+ (when error-if-not-found?
+ (error 'graph-edge-not-found-error :vertex-1 v1 :vertex-2 v2))))