Explicit computation of the index of a positive outer automorphism of the free group

Abstract

We give an algorithm for finding the index of a positive outer automorphism of the free group, and prove the algorithm exits in a finite time.

31 pages, 2 figures. v2: small error in steps (3.1.3) and (3.1.4) of the algorithm corrected. Paragraph and examples added in section 3.2.1