Christian Rüede The proof-theoretic analysis of Sigma<sub>1</sub><sup>1</sup> transfinite dependent choice. 195-234 2003 122 Ann. Pure Appl. Logic 1-3 http://dx.doi.org/10.1016/S0168-0072(03)00006-X db/journals/apal/apal122.html#Ruede03