@article{KohOl:03,
  journal = {Proc. Steklov Inst. Math},
  volume = 242,
  year = 2003,
  title = {{P}roof {M}ining: {A} {S}ystematic {W}ay of {A}nalyzing {P}roofs in
           {M}athematics},
  pages = {136--164},
  author = {Kohlenbach, Ulrich and Oliva, Paulo},
}