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obelus
An obelus (symbol: ÷, plural: obeluses or obeli) is a symbol consisting of a short horizontal line with a dot above and below. It is mainly used to represent the mathematical operation of division. It is therefore commonly called the division sign. Division may also be indicated by a horizontal line (fraction bar), or a slash.
Historically, this symbol had also been used to represent subtraction in Northern Europe.〔. Reprint of 1928 edition.〕
== History ==
The word "obelus" comes from , the Ancient Greek word for a sharpened stick, spit, or pointed pillar. This is the same root as that of the word "obelisk". Originally this sign (or a plain line) was used in ancient manuscripts to mark passages that were suspected of being corrupted or spurious. The dagger symbol, also called an obelisk, is derived from the obelus and continues to be used for this purpose.
The obelus, invented by Aristarchus to mark suspected passages in Homer, is frequent in manuscripts of the Gospel to mark just those sections, like the Pericope in John, which modern editors reject. The first corrector of א, probably the contemporary (copy-editor, rectifier, proofreader), was at pains to enclose in brackets and mark with dots for deletion two famous passages in Luke written by the original scribe which, being absent from B W 579 and the Egyptian versions, we infer were not accepted in the text at that time dominant in Alexandria, viz. the incident of the "Bloody Sweat" in Gethsemane (Lk.xxi.43 f.) and the saying "Father forgive them" (Lk.xi.34).〔Burnett Hillman Streeter, ''The Four Gospels'', London, Macmillan, 1924 () The Aristarchus referred to was presumably Aristarchus of Samothrace.〕
Although previously used for subtraction, the obelus was first used as a symbol for division in 1659 in the algebra book ''Teutsche Algebra'' by Johann Rahn. Some think that John Pell, who edited the book, may have been responsible for this use of the symbol. The usage of the obelus to represent subtraction continued in some parts of Europe (including Norway and, until fairly recently, Denmark).〔 Other symbols for division include the slash or solidus (/), and the fraction bar (the horizontal bar in a vertical fraction).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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