@inproceedings{SAT-2013-Johannsen,
	author        = "Jan Johannsen",
	booktitle     = "{Proceedings of the 16th International Conference on Theory and Applications of Satisfiability Testing}",
	doi           = "10.1007/978-3-642-39071-5_5",
	isbn          = "978-3-642-39070-8",
	pages         = "40--51",
	publisher     = "{Springer International Publishing}",
	series        = "{Lecture Notes in Computer Science}",
	title         = "{Exponential Separations in a Hierarchy of Clause Learning Proof Systems}",
	volume        = 7962,
	year          = 2013,
}