In Alan Turing's On Computable Numbers, he explains in his second paragraph the general notion of computable numbers. In doing so, he writes "In [symbol][symbol] 9, 10 I give some arguments...". I will include a screenshot of these symbols in this post. Do any of you know what these symbols mean? I guessing they are just some way of citing his paper "9, 10" which I also have no idea of. He uses this notation throughout the paper so if you happen to know the papers he is refering to, please enlighten me. Thank you.