The "big five subsystems of second-order arithmetic" in reverse arithmetic reveal the stratification of the structure of mathematics. What if any is the connection of these strata with complexity classes?
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2$\begingroup$ Even an NP problem can be solved recursively, so all the complexity of the usual classes is buried in RCA_0. Beyond that, there are obviously many maps from the five subsystems of second-order arithmetic to complexity classes that preserve (non-)inclusion, but I don't know of any that are insightful. $\endgroup$– user44143Commented Sep 19, 2017 at 5:42
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