Many of the graph algorithms, e.g., dag_shortest_paths(), combine edge weights to form distances along a path through the graph. Although the default combine functor is based on addition, quite general ones may be used. The naming of the distance_zero() named argument is apparently based on the fact that zero (0) is the identity for addition. However, for more general combine methods, zero (0) may not be an identity. Indeed, the latter, i.e., identity, not the former, i.e., zero (0), is in fact the relevant property for this argument with respect to the algorithms. Consequently, it seems that this argument is misnamed. As part of the revision of the graph library, I suggest that this named parameter be relabeled to distance_identity(). That would capture its general meaning, regardless of the nature of the combine method. Cheers, Brook