filterValid :: List -> [Graph.Edge] -> [Graph.Edge]
filterValid nl  =  filter $ \(x,y) -> IntMap.member x nl && IntMap.member y nl
filterValid :: List -> [Graph.Edge] -> [Graph.Edge]
filterValid nl  =  filter $ \(x,y) -> IntMap.member x nl && IntMap.member y nl
filterValid nl  =  filter $ \(x,y) -> IntMap.member x nl && IntMap.member y nl