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A pager (also known as a beeper or bleeper) is a wireless telecommunications device that receives and displays alphanumeric or voice messages. One-way pagers can only receive messages, while response pagers and two-way pagers can also acknowledge, reply to and originate messages using an internal transmitter.
Pagers operate as part of a paging system which includes one or more fixed transmitters (or in the case of response pagers and two-way pagers, one or more base stations), as well as a number of pagers carried by mobile users. These systems can range from a restaurant system with a single low power transmitter, to a nationwide system with thousands of high-power base stations.
Pagers were developed in the 1950s and 1960s, and became widely used by the 1980s. In the 21st century, the widespread availability of cellphones and smartphones has greatly diminished the pager industry. Nevertheless, pagers continue to be used by some emergency services and public safety personnel, because modern pager systems' coverage overlap, combined with use of satellite communications, can make paging systems more reliable than terrestrial based cellular networks in some cases, including during natural and man-made disasters. This resilience has led public safety agencies to adopt pagers over cellular and other commercial services for critical messaging.
In Japanese, it was commonly called a pocket bell (ポケットベル, poketto beru) or pokeberu (ポケベル), which is an example of wasei-eigo.
Mathematical Alphanumeric Symbols is a Unicode block comprising styled forms of Latin and Greek letters and decimal digits that enable mathematicians to denote different notions with different letter styles. The letters in various fonts often have specific, fixed meanings in particular areas of mathematics. By providing uniformity over numerous mathematical articles and books, these conventions help to read mathematical formulas. These also may be used to differentiate between concepts that share a letter in a single problem.
Unicode now includes many such symbols (in the range U+1D400–U+1D7FF). The rationale behind this is that it enables design and usage of special mathematical characters (fonts) that include all necessary properties to differentiate from other alphanumerics, e.g. in mathematics an italic "𝐴" can have a different meaning from a roman letter "A". Unicode originally included a limited set of such letter forms in its Letterlike Symbols block before completing the set of Latin and Greek letter forms in this block beginning in version 3.1.
Unicode expressly recommends that these characters not be used in general text as a substitute for presentational markup; the letters are specifically designed to be semantically different from each other. Unicode does not include a set of normal serif letters in the set. Still they have found some usage on social media, for example by people who want a stylized user name, and in email spam, in an attempt to bypass filters.
All these letter shapes may be manipulated with MathML's attribute mathvariant.
The introduction date of some of the more commonly used symbols can be found in the Table of mathematical symbols by introduction date.