question: protected void insertUniqueEdge ( Edge e ) { Edge existingEdge = edgeList . findEqualEdge ( e ) ; if ( existingEdge != null ) { Label existingLabel = existingEdge . getLabel ( ) ; Label labelToMerge = e . getLabel ( ) ; if ( ! existingEdge . isPointwiseEqual ( e ) ) { labelToMerge = new Label ( e . getLabel ( ) ) ; labelToMerge . flip ( ) ; } existingLabel . merge ( labelToMerge ) ; int mergeDelta = depthDelta ( labelToMerge ) ; int existingDelta = existingEdge . getDepthDelta ( ) ; int newDelta = existingDelta + mergeDelta ; existingEdge . setDepthDelta ( newDelta ) ; } else { edgeList . add ( e ) ; e . setDepthDelta ( depthDelta ( e . getLabel ( ) ) ) ; } }
target:  Inserted edges are checked to see if an identical edge already exists. If so, the edge is not inserted, but its label is merged with the existing edge.