reverseDependencyClosure :: GenericInstallPlan ipkg srcpkg iresult ifailure
                         -> [UnitId]
                         -> [GenericPlanPackage ipkg srcpkg iresult ifailure]
reverseDependencyClosure plan =
    map (planPkgOf plan)
  . concatMap Tree.flatten
  . Graph.dfs (planGraphRev plan)
  . map (planVertexOf plan)
reverseDependencyClosure :: GenericInstallPlan ipkg srcpkg iresult ifailure
                         -> [UnitId]
                         -> [GenericPlanPackage ipkg srcpkg iresult ifailure]
reverseDependencyClosure plan =
    map (planPkgOf plan)
  . concatMap Tree.flatten
  . Graph.dfs (planGraphRev plan)
  . map (planVertexOf plan)
reverseDependencyClosure plan =
    map (planPkgOf plan)
  . concatMap Tree.flatten
  . Graph.dfs (planGraphRev plan)
  . map (planVertexOf plan)