single value constraint
['arXiv ID', 'Prior to April 2007, the identifiers included a classification, an optional two-letter subdivision, and a 7-digit YYMMNNN year, month, and sequence number of submission in that category. E.g. gr-qc/0610068 or math.GT/0309136. After April 2007, the format was changed to a YYMM.NNNN, from 2015 an additional digit was added making the format YYMM.NNNNN', 'single value constraint', 'arXiv classification', 'arXiv ID']