This algorithm is used to generate diagrams in GPM display pages that indicate the peptides which are unlikely to be observed in a proteomics experiment. A "green" peptide is unlikely to be observed and all other peptides are "white".
For each peptide sequence, if any of the following rules are met, the peptide is rated "green":
All other peptides are "white".
The Perl code that performs this assessment in GPM is the subroutine "unlikely", found in "/thegpm-cgi/common.pl".