@articleLe Roux_Ziegler_2008, title=Singular Coverings and Non-Uniform Notions of Closed Set Computability, DOI=10.1016/j.entcs.2008.03.009, journal=Electronic Notes in Theoretical Computer Science, author=Le Roux, Stéphane and Ziegler, Martin, year=2008, pages=73–88 

@articleZiegler_2007, title=Revising Type-2 Computation and Degrees of Discontinuity, DOI=10.1016/j.entcs.2006.08.015, journal=Electronic Notes in Theoretical Computer Science, author=Ziegler, Martin, year=2007, pages=255–274