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The method of Zygalski sheets was a cryptologic technique used by the Polish Cipher Bureau before and during World War II, and during the war also by British cryptologists at Bletchley Park, to decrypt messages enciphered on German Enigma machines. The Zygalski-sheet apparatus takes its name from Polish Cipher Bureau mathematician ...
The Enigma machines combined multiple levels of movable rotors and plug cables to produce a particularly complex polyalphabetic substitution cipher.. During World War I, inventors in several countries realised that a purely random key sequence, containing no repetitive pattern, would, in principle, make a polyalphabetic substitution cipher unbreakable. [6]
At present, there is no explanation widely accepted by economists. [8] [9] [10] The Modigliani–Miller theorem suggests that the puzzle can (only) be explained by some combination of taxes, bankruptcy costs, market inefficiency (including that due to investor psychology), and asymmetric information.
Many mathematical problems have been stated but not yet solved. These problems come from many areas of mathematics, such as theoretical physics, computer science, algebra, analysis, combinatorics, algebraic, differential, discrete and Euclidean geometries, graph theory, group theory, model theory, number theory, set theory, Ramsey theory, dynamical systems, and partial differential equations.
The Publius Enigma is an Internet phenomenon and an unsolved problem that began with cryptic messages posted by a user identifying only as "Publius" to the unmoderated Usenet newsgroup alt.music.pink-floyd through the Penet remailer, a now defunct anonymous information exchange service.
The following is a list of notable unsolved problems grouped into broad areas of physics. [1]Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result.
Gear of the Antikythera mechanism, a mechanical computer from the 2nd century BCE showing a previously unknown level of complexity. An out-of-place artifact (OOPArt or oopart) is an artifact of historical, archaeological, or paleontological interest to someone that is claimed to have been found in an unusual context, which someone claims to challenge conventional historical chronology by its ...
A common example of an NP problem not known to be in P is the Boolean satisfiability problem. Most mathematicians and computer scientists expect that P ≠ NP; however, it remains unproven. [16] The official statement of the problem was given by Stephen Cook. [17]