# Is it possible to use a mathematical expression as function name?

This might seem as a silly question, but is it feasible to use a mathematical expression as the name of a function?

For example, I'm studying the cross section of Compton scattering and there is a formula for the differential cross section, which is denoted as $\frac{d\sigma}{d\Omega}$. I'd like to express the latter as a function of energy E, angle θ and atomic number Z.

If I, naively, use $\frac{d\sigma}{d\Omega}[Z\_, E\_, \theta\_] := \ldots$ I get the anticipated error:

SetDelayed::write : Tag Times in dσ/dΩ[Z_,E_,θ_] is Protected

Instead of the obvious workaround of using a name such as diffSection[Z_,E_,θ_] := ... is there any other way ?

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A big barred underscript could do? – Peltio Oct 9 '13 at 15:55

## 1 Answer

You could use the Notation package:

<< Notation
Symbolize[ParsedBoxWrapper[FractionBox["d\[Sigma]", "d\[CapitalOmega]"]]]
(d\[Sigma]/d\[CapitalOmega])[\[CapitalEpsilon]_, r_, \[Theta]_] := f[\[CapitalEpsilon], r, \[Theta]]
`

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Worked perfect! Thanks @TimothyWofford! – Zet Oct 9 '13 at 17:05