[Boost-users] Neighborhood of a subgraph

Hi, I am new to BGL and wanted to find out if there's an easy way to do the following in BoostGL: Given a subset of vertices (specified as a parameter to the function), a graph g, how does one query the neighbors of the subset that are not in the subset? Is there a function already written that I can use or an easy way to implement the above using simple building-blocks? I could maybe write my own...but I need to be making this query many many times for different subgraphs and I'd prefer to not have to check the membership within the subset many times over and over again. Any ideas will be greatly appreciated! Thanks! -Imran.