public static WeightedGraph <TValue, TWeight> .Vertex AddCyclicNeighbor <TWeight, TValue>(this WeightedGraph <TValue, TWeight> .Vertex self, TWeight weight, TValue value)
where TWeight : struct, IWeight
{
var neighbor = self.AddNeighbor(weight, value);
neighbor.AddNeighbor(weight, self.Value);
return(neighbor);
}