Systems of Logic Based on Ordinals

@article{turing-plms45,
   author = {Turing, Alan Mathison},
   doi = {10.1112/plms/s2-45.1.161},
   urlpdf = {http://plms.oxfordjournals.org/content/s2-45/1/161.full.pdf+html},
   journal = {Proceedings of the London Mathematical Society},
   number = 1,
   pages = {161--228},
   title = {Systems of Logic Based on Ordinals},
   url = {http://plms.oxfordjournals.org/content/s2-45/1/161.short},
   volume = {s2-45},
   year = 1939
}