Pigeonhole and Choice Principles. - Wolfgang Degen (Math. Log. Q., 2000)

Cumulative Higher-Order Logic as a Foundation for Set Theory. - Wolfgang Degen; Jan Johannsen (Math. Log. Q., 2000)

GOL: toward an axiomatized upper-level ontology. - Wolfgang Degen; Barbara Heller; Heinrich Herre; Barry Smith 001 (FOIS, 2001)

Rigid Unary Functions and the Axiom of Choice. - Wolfgang Degen (Math. Log. Q., 2001)

Factors of Functions, AC and Recursive Analogues. - Wolfgang Degen (Math. Log. Q., 2002)