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  The arithmetical operations of numbers, such as addition, subtraction, multiplication and division, are generalized in the branch of mathematics called abstract algebra, the study of abstract number systems such as groups, rings and fields. 
  In the baseten number system, they are written as a string of digits, with a period (decimal point) (in, for example, the US and UK) or a comma (in, for example, continental Europe) to the right of the ones place; negative real numbers are written with a preceding minus sign. 
  The existence of complex numbers was not completely accepted until the geometrical interpretation had been described by Caspar Wessel in 1799; it was rediscovered several years later and popularized by Carl Friedrich Gauss, and as a result the theory of complex numbers received a notable expansion. 
 www.oobdoo.com /wikipedia/?title=Number (3888 words) 
