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print for split '(?=[KR][^P])', 'APADPKGSTIDRPDAARTLTVHKCEQTDTRGVKEGTRNEDPQAECKPVSDVEFTITKLNVD';; ... KEGT RNEDPQAECKPVSDVEFTIT KLNVD
print for split '(?<=[KR](?!P))', 'APADPKGSTIDRPDAARTLTVHKCEQTDTRGVKEGTRNEDPQAECKPVSDVEFTITKLNVD';; ... EGTR NEDPQAECKPVSDVEFTITK LNVD