Ulrich Kohlenbach Paulo Oliva Proof mining in <i>L</i><sub>1</sub>-approximation. 1-38 2003 121 Ann. Pure Appl. Logic 1 http://dx.doi.org/10.1016/S0168-0072(02)00081-7 db/journals/apal/apal121.html#KohlenbachO03