“…Lie bialgebra structures on the Witt algebra and the Virasoro algebra were considered and classified in [21,25]. Since then, Lie bialgebra structures as well as their quantizations on some infinitedimensional graded Lie algebras, in particular those containing the Virasoro algebra (or its q-analog) have been extensively studied (e.g., [7,13,17,19,22,23,[25][26][27][28]). We have noticed that, for the above-mentioned infinite-dimensional graded Lie algebras, the Virasoro algebra plays a very crucial role in determining their bialgebra structures because of the fact that the modules of the intermediate series of the Virasoro algebra have relatively simple module structures (see, e.g., [24]).…”