There are infinitely many variants of the notion of Kan fibration that, together with suitable choices of cofibrations and the usual notion of weak equivalence of simplicial sets, ...
We upgrade the light Dialectica interpretation [6] by adding two more light universal quantifiers, which are both semi-computational and semi-uniform and complement each other. An...
We show that each of the five basic theories of second order arithmetic that play a central role in reverse mathematics has a natural counterpart in the language of nonstandard ari...
We show that there is a model of ZF in which the Borel hierarchy on the reals has length 2. This implies that 1 has countable cofinality, so the axiom of choice fails very badly i...
In Zermelo-Fraenkel set theory with the axiom of choice every set has the same cardinal number as some ordinal. Von Rimscha has weakened this condition to "Every set has the s...