"In this paper Turing gives a topological argument that every written alphabet must be finite." I searched Turing's paper and the word "alphabet" does not appe

"In this paper Turing gives a topological argument that every written alphabet must be finite." I searched Turing's paper and the word "alphabet" does not appear. I guess the author interprets Turing's use of "symbol" as an "alphabet". Can anyone familiar with Turing's paper clarify?