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In mathematics, abstract nonsense, general abstract nonsense, generalized abstract nonsense, and general nonsense are nonderogatory terms used by mathematicians to describe long, theoretical parts of a proof they skip over when readers are expected to be familiar with them. These terms are mainly used for abstract methods related to category theory and homological algebra. More generally, "abstract nonsense" may refer to a proof that relies on category-theoretic methods, or even to the study of category theory itself.

A micromort (from micro- and mortality) is a unit of risk defined as one-in-a-million chance of death. Micromorts can be used to measure riskiness of various day-to-day activities. A microprobability is a one-in-a million chance of some event; thus a micromort is the microprobability of death. The micromort concept was introduced by Ronald A. Howard who pioneered the modern practice of decision analysis.

Micromorts for future activities can only be rough assessments as specific circumstances will always have an impact. However past historical rates of events can be used to provide a ball park, average figure.

Robert's Rules of Order, often simply referred to as Robert's Rules, is a manual of parliamentary procedure by U.S. Army officer Henry Martyn Robert. "The object of Rules of Order is to assist an assembly to accomplish the work for which it was designed [...] Where there is no law [...] there is the least of real liberty". The term "Robert's Rules of Order" is also used more generically to refer to any of the more recent editions, by various editors and authors, based on any of Robert's original editions, and the term is used more generically in the United States to refer to parliamentary procedure.

Robert's manual was first published in 1876 as an adaptation of the rules and practice of the United States Congress to the needs of non-legislative societies. Robert's Rules is the most widely used manual of parliamentary procedure in the United States. It governs the meetings of a diverse range of organizations—including church groups, county commissions, homeowners associations, nonprofit associations, professional societies, school boards, and trade unions—that have adopted it as their parliamentary authority. Robert published four editions of the manual before his death in 1923, the last being the thoroughly revised and expanded Fourth Edition published as Robert's Rules of Order Revised in May 1915.

An untouchable number is a positive integer that cannot be expressed as the sum of all the proper divisors of any positive integer (including the untouchable number itself). That is, these numbers are not in the image of the aliquot sum function. Their study goes back at least to Abu Mansur al-Baghdadi (circa 1000 AD), who observed that both 2 and 5 are untouchable.

The Corrupted Blood incident was a virtual pandemic in the MMORPG World of Warcraft, which began on September 13, 2005, and lasted for one week. The epidemic began with the introduction of the new raid Zul'Gurub and its end boss Hakkar the Soulflayer. When confronted and attacked, Hakkar would cast a hit point-draining and highly contagious debuff spell called "Corrupted Blood" on players.

The spell, intended to last only seconds and function only within the new area of Zul'Gurub, soon spread across the virtual world by way of an oversight that allowed pets and minions to take the affliction out of its intended confines. By both accidental and purposeful intent, a pandemic ensued that quickly killed lower-level characters and drastically changed normal gameplay, as players did what they could do to avoid infection. Despite measures such as programmer-imposed quarantines, and the players' abandoning of densely populated cities (or even just not playing the game), it lasted until a combination of patches and resets of the virtual world finally controlled the spread.

The conditions and reactions of the event attracted the attention of epidemiologists for its implications of how human populations could react to a real-world epidemic.

Resistor–transistor logic (RTL) (sometimes also transistor–resistor logic (TRL)) is a class of digital circuits built using resistors as the input network and bipolar junction transistors (BJTs) as switching devices. RTL is the earliest class of transistorized digital logic circuit; it was succeeded by diode–transistor logic (DTL) and transistor–transistor logic (TTL).

RTL circuits were first constructed with discrete components, but in 1961 it became the first digital logic family to be produced as a monolithic integrated circuit. RTL integrated circuits were used in the Apollo Guidance Computer, whose design begun in 1961 and which first flew in 1966.

Height can significantly influence success in sports, depending on how the design of the sport is linked to factors that are height-biased due to physics and biology. The balance of the intricate array of links will determine the degree to which height plays a role in success, if any.

In mathematics, the Weierstrass function is an example of a real-valued function that is continuous everywhere but differentiable nowhere. It is an example of a fractal curve. It is named after its discoverer Karl Weierstrass.

The Weierstrass function has historically served the role of a pathological function, being the first published example (1872) specifically concocted to challenge the notion that every continuous function is differentiable except on a set of isolated points. Weierstrass's demonstration that continuity did not imply almost-everywhere differentiability upended mathematics, overturning several proofs that relied on geometric intuition and vague definitions of smoothness. These types of functions were denounced by contemporaries: Henri Poincaré famously described them as "monsters" and called Weierstrass' work "an outrage against common sense", while Charles Hermite wrote that they were a "lamentable scourge". The functions were difficult to visualize until the arrival of computers in the next century, and the results did not gain wide acceptance until practical applications such as models of Brownian motion necessitated infinitely jagged functions (nowadays known as fractal curves).

The frog galvanoscope was a sensitive electrical instrument used to detect voltage in the late eighteenth and nineteenth centuries. It consists of skinned frog's leg with electrical connections to a nerve. The instrument was invented by Luigi Galvani and improved by Carlo Matteucci.

The frog galvanoscope, and other experiments with frogs played a part in the dispute between Galvani and Alessandro Volta over the nature of electricity. The instrument is extremely sensitive and continued to be used well into the nineteenth century, even after electromechanical meters came into use.

In mathematical statistics, the Kullback–Leibler divergence (also called relative entropy and I-divergence), denoted ${\displaystyle D_{\text{KL}}(P\parallel Q)}$, is a type of statistical distance: a measure of how one probability distribution P is different from a second, reference probability distribution Q. A simple interpretation of the KL divergence of P from Q is the expected excess surprise from using Q as a model when the actual distribution is P. While it is a distance, it is not a metric, the most familiar type of distance: it is not symmetric in the two distributions (in contrast to variation of information), and does not satisfy the triangle inequality. Instead, in terms of information geometry, it is a type of divergence, a generalization of squared distance, and for certain classes of distributions (notably an exponential family), it satisfies a generalized Pythagorean theorem (which applies to squared distances).

In the simple case, a relative entropy of 0 indicates that the two distributions in question have identical quantities of information. Relative entropy is a nonnegative function of two distributions or measures. It has diverse applications, both theoretical, such as characterizing the relative (Shannon) entropy in information systems, randomness in continuous time-series, and information gain when comparing statistical models of inference; and practical, such as applied statistics, fluid mechanics, neuroscience and bioinformatics.