public bool contains_edge(edge_store the_edge)
 {
     // find whether the edge belongs to the triangle
     if (the_edge.Equals_without_orientation(this._e1) == true ||
         the_edge.Equals_without_orientation(this._e2) == true ||
         the_edge.Equals_without_orientation(this._e3) == true)
     {
         return(true);
     }
     return(false);
 }
 public point_store get_other_pt(edge_store the_edge)
 {
     // Returns the third vertex of this triangle which is not part of the given edge
     if (the_edge.Equals_without_orientation(this.e1) == true)
     {
         return(this.e2.find_common_pt(this.e3));
     }
     else if (the_edge.Equals_without_orientation(this.e2) == true)
     {
         return(this.e3.find_common_pt(this.e1));
     }
     else if (the_edge.Equals_without_orientation(this.e3) == true)
     {
         return(this.e1.find_common_pt(this.e2));
     }
     return(null);
 }