plus signPlusSign2007-10-22 11:01:052007-10-30 05:08:30Definitionaddition% this is the default PlanetMath preamble. as your knowledge
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There are two main uses of the {\em plus sign} ``$+$'' (which is a simplified form of ``\&'') in the mathematics and the applying sciences:
\begin{itemize}
\item The original use is as the sign for the binary operation {\em addition} of numbers and other elements of rings and algebras, vectors, etc.:
$$a\!+\!b\; := \mbox{\, the sum of\, } a \mbox{\, and\, }b$$
\item There is also a special use for the unary operation {\em identity mapping} concerning numbers and other ring elements:
$$+a\; :=\; a \mbox{\; (for all } a)$$
\end{itemize}