let sortedKeys2 = Array(parents.keys).sorted { lhs, rhs in
        let lhsContent = parents[lhs] ?? []
        let rhsContent = parents[rhs] ?? []
        switch (lhsContent.isEmpty, rhsContent.isEmpty) {
        case (true, true):
            return rhs > lhs
        case (true, false):
            return true
        case (false, true):
            return false
        case (false, false):
            return rhsContent.contains(lhs)
        }
    }