packagesThatDependOn :: GenericInstallPlan ipkg srcpkg iresult ifailure
                     -> UnitId
                     -> [GenericPlanPackage ipkg srcpkg iresult ifailure]
packagesThatDependOn plan pkgid = map (planPkgOf plan)
                          . tail
                          . Graph.reachable (planGraphRev plan)
                          . planVertexOf plan
                          $ pkgid
packagesThatDependOn :: GenericInstallPlan ipkg srcpkg iresult ifailure
                     -> UnitId
                     -> [GenericPlanPackage ipkg srcpkg iresult ifailure]
packagesThatDependOn plan pkgid = map (planPkgOf plan)
                          . tail
                          . Graph.reachable (planGraphRev plan)
                          . planVertexOf plan
                          $ pkgid
packagesThatDependOn plan pkgid = map (planPkgOf plan)
                          . tail
                          . Graph.reachable (planGraphRev plan)
                          . planVertexOf plan
                          $ pkgid