An ELS skip specification σ specifies the search protocol for finding ELSs of a key word. α specifies the minimum absolute skip ELSs can have and specifies how the maximum skip of an ELS will be determined. The maximum skip can be determined in three ways: fixed largest skip, largest possible skip, and expected number.
The fixed largest skip criterion just specifies an integer M. All ELSs of absolute skip no larger than M will be found in each text searched.The largest possible skip criterion specifies that the largest skip an ELS can have is the largest possible skip it can have in the text. If the number of characters of the key word is N and the number of characters in the text is Z, then the largest possible skip Smax for searching for ELSs of the given key word is the largest integer smaller than or equal to (N-1)/(Z-1).
The expected number criterion specifies that the largest skip, Smax, an ELS of key word w can have is set so that in the random letter permuted text population, the expected number of ELSs found by the search is just larger than the given expected number criterion N.