public Edge findEqualEdge(Edge e){
  OrientedCoordinateArray oca=new OrientedCoordinateArray(e.getCoordinates());
  Edge matchEdge=(Edge)ocaMap.get(oca);
  return matchEdge;
}

public Edge findEqualEdge ( Edge e ) { OrientedCoordinateArray oca = new OrientedCoordinateArray ( e . getCoordinates ( ) ) ; Edge matchEdge = ( Edge ) ocaMap . get ( oca ) ; return matchEdge ; }
if there is an edge equal to e already in the list , return it . otherwise return null .
