Le Roux, Stéphane, and Martin Ziegler. “Singular Coverings and Non-Uniform Notions of Closed Set Computability.”https://doi.org/10.1016/j.entcs.2008.03.009__Electronic Notes in Theoretical Computer Science, 2008, 73–88.https://doi.org/10.1016/j.entcs.2008.03.009 .

Ziegler, Martin. “Revising Type-2 Computation and Degrees of Discontinuity.”https://doi.org/10.1016/j.entcs.2006.08.015__Electronic Notes in Theoretical Computer Science, 2007, 255–74.https://doi.org/10.1016/j.entcs.2006.08.015 .