edgeLabelE :: Edge -> GS Label
edgeLabelE e = do l <- getEdgeLabel $ edgeLabelIndex e
                  return $ MB.fromMaybe (error "incorrect edge in function edgeLabel") l
edgeLabelE :: Edge -> GS Label
edgeLabelE e = do l <- getEdgeLabel $ edgeLabelIndex e
                  return $ MB.fromMaybe (error "incorrect edge in function edgeLabel") l
edgeLabelE e = do l <- getEdgeLabel $ edgeLabelIndex e
                  return $ MB.fromMaybe (error "incorrect edge in function edgeLabel") l