Editing Slash (punctuation) (section)

==== Combining slash ====
Slashes may also be used as a [[combining character]] in mathematical formulae. The most important use of this is that combining a slash with a [[binary relation|relation]] negates it, producing e.g. 'not equal' <math>\neq</math> as negation of <math>=</math> or 'not in' <math>\notin</math> as negation of <math>\in</math>; these slashed relation symbols are always implicitly defined in terms of the non-slashed base symbol. The graphical form of the negation slash is mostly the same as for a division slash, except in some cases where that would look odd; the negation <math>\nmid</math> of <math>\mid</math> (divides) and negation <math>\nsim</math> of <math>\sim</math> (various meanings) customarily both have their negations slashes less steep and in particular shorter than the usual one.

The [[Feynman slash notation]] is an unrelated use of combining slashes, mostly seen in [[quantum field theory]]. This kind of combining slash takes a vector base symbol and converts it to a matrix quantity. Technically this notation is a shorthand for contracting the vector with the [[gamma matrix|Dirac gamma matrices]], so <math>A\!\!\!/ = \gamma^\mu A_\mu</math>; what one gains is not only a more compact formula, but also not having to allocate a letter as the contracted index.