Hi, I need to use the topological_sort BGL algorithm. This algorithm needs either that the graph has an internal vertex index property or that you provide a property map for it. I'd like to perform conditional compilation, so that I only build and provide the vertex index property map when it's needed, and the internal index property of the graph when it has it. For example, for an adjacency_list with vecS for VertexList, the property already exists in the graph and I wouldn't like to provide a property map for it. But if I choose listS for VertexList, there isn't such internal property and I need to provide the property map. As I don't know what Graph implementation my template will be provided, I need to find a way to know at compile time if that graph has the internal index property or not. Is there any (documented?) way to do it? This is the concrete information I need right now, but, if possible, I'd like to know how to find out if the graph has any concrete internal property, and not only the index one. Thanks, Juan