Template:Individual-TLP-paragraph-en-5.2522

5.2522 The general term of the formal series a, O'a, O'O'a, ... I write thus: “[a, x, O'x]”. This expression in brackets is a variable. The first term of the expression is the beginning of the formal series, the second the form of an arbitrary term x of the series, and the third the form of that term of the series which immediately follows x.