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 ?

  • $\begingroup$ A big barred underscript could do? $\endgroup$
    – Peltio
    Commented Oct 9, 2013 at 15:55

1 Answer 1


You could use the Notation package:

<< Notation`
Symbolize[ParsedBoxWrapper[FractionBox["dσ", "dΩ"]]]
(dσ/dΩ)[Ε_, r_, θ_] := f[Ε, r, θ]

Notation package used to make a complicated symbol

  • $\begingroup$ Worked perfect! Thanks @TimothyWofford! $\endgroup$
    – stathisk
    Commented Oct 9, 2013 at 17:05

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