B. Lellmann et al.:
"Standard Sequent Calculi for Lewis' Logics of Counterfactuals";
in: "Logics in Artificial Intelligence, 15th European Conference, JELIA 2016, Larnaca, Cyprus, November 9-11", 10021; Springer International Publishing, Heidelberg, 2016, ISBN: 978-3-319-48757-1, 272 - 287.
http://publik.tuwien.ac.at/files/publik_254673.pdf