Matteo Viale (University of Turin)

Absolute Model Companionship, the AMC-spectrum of set theory, and the continuum problem

We introduce a classification tool for mathematical theories based on Robinson's notion of model companionship; roughly the idea is to attach to a mathematical theory $T$ those signatures $L$ such that $T$ as axiomatized in $L$ admits a model companion. We also introduce a slight strengthening of model companionship (absolute model companionship - AMC) which characterize those model companionable $L$-theories $T$ whose model companion is axiomatized by the $\Pi_2$-sentences for $L$ which are consistent with the universal and existential theory of any $L$-model of $T$. We use the above to analyze set theory, and we show that the above classification tools can be used to extract (surprising?) information on the continuum problem. Slides