1. Functional analysis in weak subsystems of second order arithmetic;Brown,1987
2. Which set existence axioms are needed to prove the Hahn-Banach Theorem for separable Banach spaces?;Brown;Ann. Pure Appl. Logic,1986
3. Some systems of second order arithmetic and their use;Friedman,1975
4. Systems of second order arithmetic with restricted induction;Friedman;J. Symbolic Logic,1976