2021/02/09 by Goldberg, Gabriel · 1 citation
#FOS: Mathematics #Logic (math.LO)
paper · doi:10.48550/arxiv.2102.04677
Assuming the Generalized Continuum Hypothesis, this paper answers the question: when is the tensor product of two ultrafilters equal to their Cartesian product? It is necessary and sufficient that their Cartesian product is an ultrafilter; that the two ultrafilters commute in the tensor product; that for all cardinals λ, one of the ultrafilters is both λ-indecomposable and λ+-indecomposable; that the ultrapower embedding associated to each ultrafilter restricts to a definable embedding of the ultrapower of the universe associated to the other.