-- | The states of packages have that depend on each other must respect
-- this relation. That is for very case where package @a@ depends on
-- package @b@ we require that @dependencyStatesOk a b = True@.
--
stateDependencyRelation :: GenericPlanPackage ipkg srcpkg iresult ifailure
                        -> GenericPlanPackage ipkg srcpkg iresult ifailure
                        -> Bool
stateDependencyRelation (PreExisting _) (PreExisting _)   = True
stateDependencyRelation :: GenericPlanPackage ipkg srcpkg iresult ifailure
                        -> GenericPlanPackage ipkg srcpkg iresult ifailure
                        -> Bool
stateDependencyRelation (PreExisting _) (PreExisting _)   = True
stateDependencyRelation (PreExisting _) (PreExisting _)   = True