David Belanger, Cornell University
“Disjunctions in reverse mathematics”
The main question of reverse mathematics is: ”What axioms are needed are needed to prove a given theorem of ordinary math?” Implicit is the assumption that if there is more than one proof, there is a best proof among them using axioms weaker than all the rest. We consider statements where this is true only on a technicality: there are two proofs using different axioms A and B, and the best proof simply chooses between them using A ∨ B. Examples come from effective model theory.