public Vertex GetOtherVertex(Edge3 e)
 {
     if (!e.Has(v0))
     {
         return(v0);
     }
     else if (!e.Has(v1))
     {
         return(v1);
     }
     return(v2);
 }
        public Triangle3(
            Vertex v0, Vertex v1, Vertex v2,
            Edge3 e0, Edge3 e1, Edge3 e2
            )
        {
            this.v0 = v0;
            this.v1 = v1;
            this.v2 = v2;

            this.e0 = e0;
            this.e1 = e1;
            this.e2 = e2;
        }