1. Concept: For the SAM on the string S, it will contain S contains all and only the substring.
2. The key (endpos class): for a sub-string T, which the original string of dots appearing in the right position for its collection set endpos.
For a substring has its own unique set of endpos, endpos for a class contains a plurality of strings.
Endpos on any of a class string, it contains the sub-strings each other suffix .