Other types of classical ciphers are sometimes used to create cryptograms. Fill-Ins are common in puzzle magazines along with word searches, cryptograms, and other logic puzzles. The letters included four cryptograms (or ciphers). Cryptograms and extras, as well as catchall categories for rule-breaking puzzles, were added later. Another similar concept is that of undeciphered cryptograms, or cipher messages. Bigram frequency attacks can be used in cryptography to solve cryptograms. The chapters include a question mark, poems, rituals, instructions, and obscure allusions and cryptograms. Bellaso challenged his detractors to solve some cryptograms encrypted according to his guidelines. The bag referenced his love alphabet, "Daligramme", made up of eight cryptograms. Of the four cryptograms sent, only one has been definitively solved. It also helped popularize cryptograms and secret writing. Example of dynamic, transaction-specific tokens include cryptograms used in the EMV specification. In his review, he likened the album to a "tempered" version of Deerhunter's "Cryptograms". Spring Hall Convert' [from "Cryptograms"] was like that. The Zodiac Killer sent four cryptograms to police while he was still active.