FIX to Indexing Highly Repetitive String Collections, Part I: Repetitiveness Measures

Level: Medium

In Section 3.9, I say that it is enough to make an attractor with the explicit positions of the macro scheme. This is an error, since this set is easily made of the alphabet size. A substring could cross a phrase boundary without contanining an explicit symbol position, and the argument would not work.

Instead, we can choose the first position of each block to form the attractor. This is of size b and now the argument is correct.

Noted by Hideo Bannai.