Hi, I'm using Boost Graph Library (BGL), and I need a null edge. For years I was using G::edge_descriptor(), i.e., a default-constructed edge descriptor, and the code was working. However, I wonder if it is correct. Are all default-constructed edges equal? If I get a default-constructed edge descriptor e1 at some point in code, and another default-constructed edge descriptor e2 at some other point in code, will there descriptors always equal, i.e., will e1 == e2 always hold? Is it guaranteed that a default-constructed edge does not refer to an existing edge in a graph? Best, Irek