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An arrow is a graphical symbol such as ← or →, used to point or indicate direction, being in its simplest form a line segment with a triangle affixed to one end, and in more complex forms a representation of an actual arrow (e.g. (unicode:➵) U+27B5). The direction indicated by an arrow is the one along the length of the line towards the end capped by a triangle. The typographical symbol develops in the 18th century. Its use is comparable to that of the older (medieval) manicule (pointing hand, ☞). Also comparable is the use of a fleur-de-lis symbol indicating north in a compass rose by Pedro Reinel (c. 1504). An early arrow symbol is found in an illustration of Bernard Forest de Bélidor's treatise ''L'architecture hydraulique'', printed in France in 1737. The arrow is here used to illustrate the direction of the flow of water and of the water wheel's rotation. At about the same time, arrow symbols were used to indicate the flow of rivers in maps. A trend towards abstraction, in which the arrow's fletching is removed, can be observed in the mid-to-late 19th century. In a further abstraction of the symbol, John Richard Green's ''A Short History of the English People'' of 1874 contained maps by cartographer Emil Reich, which indicated army movements by curved lines, with solid triangular arrowheads placed intermittently along the lines. Use of arrow symbols in mathematical notation originates in the early 20th century. David Hilbert in 1922 introduced the arrow symbol representing logical implication. The double-headed arrow representing logical equivalence was introduced by Albrecht Becker in ''Die Aristotelische Theorie der Möglichkeitsschlüsse'', Berlin, 1933. ==Arrows in Unicode== In Unicode, the block Arrows occupies the hexadecimal range U+2190–U+21FF, as described below. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Arrow (symbol)」の詳細全文を読む スポンサード リンク
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