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🔗 Computing

FRACTRAN is a Turing-complete esoteric programming language invented by the mathematician John Conway. A FRACTRAN program is an ordered list of positive fractions together with an initial positive integer input n. The program is run by updating the integer n as follows:

1. for the first fraction f in the list for which nf is an integer, replace n by nf
2. repeat this rule until no fraction in the list produces an integer when multiplied by n, then halt.

Conway 1987 gives the following formula for primes in FRACTRAN:

${\displaystyle \left({\frac {17}{91}},{\frac {78}{85}},{\frac {19}{51}},{\frac {23}{38}},{\frac {29}{33}},{\frac {77}{29}},{\frac {95}{23}},{\frac {77}{19}},{\frac {1}{17}},{\frac {11}{13}},{\frac {13}{11}},{\frac {15}{2}},{\frac {1}{7}},{\frac {55}{1}}\right)}$

Starting with n=2, this FRACTRAN program generates the following sequence of integers:

2, 15, 825, 725, 1925, 2275, 425, 390, 330, 290, 770, ... (sequence A007542 in the OEIS)

After 2, this sequence contains the following powers of 2:

${\displaystyle 2^{2}=4,\,2^{3}=8,\,2^{5}=32,\,2^{7}=128,\,2^{11}=2048,\,2^{13}=8192,\,2^{17}=131072,\,2^{19}=524288,\,\dots }$ (sequence A034785 in the OEIS)

which are the prime powers of 2.

🔗 Science Fiction

"Computers Don't Argue" is a 1965 science fiction short story by American writer Gordon R. Dickson, about the dangers of relying too strongly upon computers. It was nominated for a Nebula Award in 1966.

🔗 Computing 🔗 Africa 🔗 Ancient Egypt 🔗 Novels 🔗 Novels/Science fiction 🔗 Science Fiction 🔗 Women writers 🔗 Egypt

The Mummy! A Tale of the Twenty-Second Century is an 1827 three-volume novel written by Jane Webb (later Jane C. Loudon). It concerns the Egyptian mummy of Cheops, who is brought back to life in the year 2126. The novel describes a future filled with advanced technology, and was the first English-language story to feature a reanimated mummy.

After her father's death, making her an orphan at the age of 17, Webb found that:

on the winding up of his affairs that it would be necessary to do something for my support. I had written a strange, wild novel, called the Mummy, in which I had laid the scene in the twenty-second century, and attempted to predict the state of improvement to which this country might possibly arrive.

She may have drawn inspiration from the general fashion for anything pharaonic, inspired by the French researches during the Napoleonic invasion of Egypt; the 1821 public unwrappings of Egyptian mummies in a theatre near Piccadilly, which she may have attended as a girl; and, very likely, the 1818 novel by Mary Shelley, Frankenstein; or, The Modern Prometheus. As Shelley had written of Frankenstein's creation, "A mummy again endued with animation could not be so hideous as that wretch," which may have triggered her later concept. In any case, at many points she deals in greater clarity with elements from the earlier book such as the loathing for the much-desired object and the immediate arrest for crime and attempt to lie one's way out of it. However, unlike the Frankenstein monster, the hideous revived Cheops is not shuffling around dealing out horror and death, but giving canny advice on politics and life to those who befriend him. In some ways The Mummy! may be seen as her reaction to themes in Frankenstein: her mummy specifically says he is allowed life only by divine favour, rather than being indisputably vivified only by mortal science, and so on, as Hopkins' 2003 essay covers in detail.

Unlike many early science fiction works (Shelley's The Last Man, and The Reign of King George VI, 1900–1925, written anonymously in 1763), Loudon did not portray the future as her own day with only political changes. She filled her world with foreseeable changes in technology, society, and even fashion. The hero, Edric Montague, lived in a peaceful and Catholic England under the rule of Queen Claudia. Her court ladies wear trousers and hair ornaments of controlled flame. Surgeons and lawyers may be steam-powered automatons. Air travel, by balloon, is commonplace. A kind of Internet is predicted in it. Besides trying to account for the revivification of the mummy in scientific terms—galvanic shock rather than incantations—"she embodied ideas of scientific progress and discovery, that now read like prophecies" to those later in the 19th century. Many of the incidents in the book can be seen as satirical or humorous. Her social attitudes have resulted in this book being ranked among feminist novels.

The Mummy!: Or a Tale of the Twenty-Second Century was published anonymously in 1827 by Henry Colburn in three volumes, as was usual in that day so that each small volume could be easily carried around. It drew many favourable reviews, including one in 1829 in The Gardener's Magazine on the inventions proposed in it. In 1830, the 46-year-old reviewer, John Claudius Loudon, sought out the 22-year-old Webb, and they married the next year.

🔗 Novels 🔗 Novels/19th century 🔗 Novels/Science fiction 🔗 New Zealand 🔗 Sociology

Erewhon: or, Over the Range () is a novel by English writer Samuel Butler, first published anonymously in 1872, set in a fictional country discovered and explored by the protagonist. The book is a satire on Victorian society.

The first few chapters of the novel dealing with the discovery of Erewhon are in fact based on Butler's own experiences in New Zealand, where, as a young man, he worked as a sheep farmer on Mesopotamia Station for about four years (1860–64), and explored parts of the interior of the South Island and wrote about in his A First Year in Canterbury Settlement (1863).

The novel is one of the first to explore ideas of artificial intelligence, as influenced by Darwin's recently published On the Origin of Species (1859) and the machines developed out of the Industrial Revolution (late 18th to early 19th centuries). Specifically, it concerns itself, in the three-chapter "Book of the Machines", with the potentially dangerous ideas of machine consciousness and self-replicating machines.

🔗 Brands 🔗 Electronics

The Capacitance Electronic Disc (CED) is an analog video disc playback system developed by RCA, in which video and audio could be played back on a TV set using a special needle and high-density groove system similar to phonograph records.

First conceived in 1964, the CED system was widely seen as a technological success which was able to increase the density of a long-playing record by two orders of magnitude. Despite this achievement, the CED system fell victim to poor planning, various conflicts with RCA management, and several technical difficulties that slowed development and stalled production of the system for 17 years—until 1981, by which time it had already been made obsolete by laser videodisc (DiscoVision, later called LaserVision and LaserDisc) as well as Betamax and VHS video cassette formats. Sales for the system were nowhere near projected estimates. In the spring of 1984, RCA announced it was discontinuing player production, but continuing the production of videodiscs until 1986, losing an estimated $600 million in the process. RCA had initially intended to release the SKT425 CED player with their high end Dimensia system in late 1984, but cancelled CED player production prior to the Dimensia system's release.

The format was commonly known as "videodisc", leading to much confusion with the contemporaneous LaserDisc format. LaserDiscs are read optically with a laser beam, whereas CED discs are read physically with a stylus (similar to a conventional gramophone record). The two systems are mutually incompatible.

RCA used the brand "SelectaVision" for the CED system, a name also used for some early RCA brand VCRs, and other experimental projects at RCA.

The Leary–Lettvin debate was a May 3, 1967 debate between Dr. Jerome Lettvin, a medical doctor and professor at MIT, and Dr. Timothy Leary, a licensed psychologist, about the merits and dangers of the hallucinogenic drug LSD. It took place in the Kresge Auditorium at the Massachusetts Institute of Technology.

🔗 Mathematics

The potato paradox is a mathematical calculation that has a counter-intuitive result. The Universal Book of Mathematics states the problem as follows:

Fred brings home 100 kg of potatoes, which (being purely mathematical potatoes) consist of 99% water. He then leaves them outside overnight so that they consist of 98% water. What is their new weight? The surprising answer is 50 kg.

In Quine's classification of paradoxes, the potato paradox is a veridical paradox.

🔗 Cryptography 🔗 Cryptography/Computer science

In cryptography a blind signature, as introduced by David Chaum, is a form of digital signature in which the content of a message is disguised (blinded) before it is signed. The resulting blind signature can be publicly verified against the original, unblinded message in the manner of a regular digital signature. Blind signatures are typically employed in privacy-related protocols where the signer and message author are different parties. Examples include cryptographic election systems and digital cash schemes.

An often-used analogy to the cryptographic blind signature is the physical act of a voter enclosing a completed anonymous ballot in a special carbon paper lined envelope that has the voter's credentials pre-printed on the outside. An official verifies the credentials and signs the envelope, thereby transferring their signature to the ballot inside via the carbon paper. Once signed, the package is given back to the voter, who transfers the now signed ballot to a new unmarked normal envelope. Thus, the signer does not view the message content, but a third party can later verify the signature and know that the signature is valid within the limitations of the underlying signature scheme.

Blind signatures can also be used to provide unlinkability, which prevents the signer from linking the blinded message it signs to a later un-blinded version that it may be called upon to verify. In this case, the signer's response is first "un-blinded" prior to verification in such a way that the signature remains valid for the un-blinded message. This can be useful in schemes where anonymity is required.

Blind signature schemes can be implemented using a number of common public key signing schemes, for instance RSA and DSA. To perform such a signature, the message is first "blinded", typically by combining it in some way with a random "blinding factor". The blinded message is passed to a signer, who then signs it using a standard signing algorithm. The resulting message, along with the blinding factor, can be later verified against the signer's public key. In some blind signature schemes, such as RSA, it is even possible to remove the blinding factor from the signature before it is verified. In these schemes, the final output (message/signature) of the blind signature scheme is identical to that of the normal signing protocol.

🔗 Mathematics

Reverse mathematics is a program in mathematical logic that seeks to determine which axioms are required to prove theorems of mathematics. Its defining method can briefly be described as "going backwards from the theorems to the axioms", in contrast to the ordinary mathematical practice of deriving theorems from axioms. It can be conceptualized as sculpting out necessary conditions from sufficient ones.

The reverse mathematics program was foreshadowed by results in set theory such as the classical theorem that the axiom of choice and Zorn's lemma are equivalent over ZF set theory. The goal of reverse mathematics, however, is to study possible axioms of ordinary theorems of mathematics rather than possible axioms for set theory.

Reverse mathematics is usually carried out using subsystems of second-order arithmetic, where many of its definitions and methods are inspired by previous work in constructive analysis and proof theory. The use of second-order arithmetic also allows many techniques from recursion theory to be employed; many results in reverse mathematics have corresponding results in computable analysis. Recently, higher-order reverse mathematics has been introduced, in which the focus is on subsystems of higher-order arithmetic, and the associated richer language.

The program was founded by Harvey Friedman (1975, 1976) and brought forward by Steve Simpson. A standard reference for the subject is (Simpson 2009), while an introduction for non-specialists is (Stillwell 2018). An introduction to higher-order reverse mathematics, and also the founding paper, is (Kohlenbach (2005)).