670 notes - Ohio State University

The elements of this group are “words” in the four symbols a, b, a–1, and b–1, subject to the requirement that a and a–1 may not be adjacent, nor may b and b–1. The identity element is the empty word, which (to make it visible) we denote by the special symbol 1. To multiply words, concatenate them, then cancel pairs as necessary. ................
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