plus sign

There are two main uses of the plus sign “ $+$ ” (which is a simplified form of “&”) in the mathematics and the applying sciences:

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The original use is as the sign for the binary operation addition of numbers and other elements of rings and algebras, vectors, etc.:

$a\!+\!b\;:=\mbox{\, the sum of\, }a\mbox{\, and\, }b$
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There is also a special use for the unary operation identity mapping concerning numbers and other ring elements:

$+a\;:=\;a\mbox{\; (for all }a)$