convert/elementary converts, when possible, the special functions in an expression into elementary transcendental functions. The elementary transcendental functions are

FunctionAdvisor( elementary );

The 26 functions in the "elementary" class are:

$\left[\arccos \,\mathrm{arccosh}\,\mathrm{arccot}\,\mathrm{arccoth}\,\mathrm{arccsc}\,\mathrm{arccsch}\,\mathrm{arcsec}\,\mathrm{arcsech}\,\arcsin \,\mathrm{arcsinh}\,\arctan \,\mathrm{arctanh}\,\cos \,\cosh \,\cot \,\coth \,\csc \,\mathrm{csch}\,\exp \,\ln \,\sec \,\mathrm{sech}\,\sin \,\sinh \,\tan \,\tanh \right]$

$\mathrm{hypergeom}\left(\left[3\right]\,\left[4\right]\,9x^{\frac{1}{6}}\right)$

$\mathrm{hypergeom}\left(\left[3\right]\,\left[4\right]\,9x^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$6$}\right.}\right)$

$\mathrm{convert}\left(\,\mathrm{elementary}\right)$

$\frac{\left(2-18x^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$6$}\right.}+81x^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right.}\right){\ⅇ}^{9x^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$6$}\right.}}}{243\sqrt{x}}-\frac{2}{243\sqrt{x}}$

$\mathrm{WhittakerM}\left(0\,\frac{1}{2}\,z\right)$

$\mathrm{WhittakerM}\left(0\,\frac{1}{2}\,z\right)$

$\mathrm{convert}\left(\,\mathrm{elementary}\right)$

$-2\mathrm{I}\sin \left(\frac{\mathrm{I}}{2}z\right)$

$\mathrm{WhittakerM}\left(\mathrm{\mu }\,\mathrm{\nu }\,0\right)$

$\mathrm{WhittakerM}\left(\mathrm{\mu }\,\mathrm{\nu }\,0\right)$

$\mathrm{convert}\left(\,\mathrm{elementary}\right)$

$0$

$\mathrm{Ei}\left(-1\,z\right)$

${\mathrm{Ei}}_{\mathrm{-1}}\left(z\right)$

$\mathrm{convert}\left(\,\mathrm{elementary}\right)$

$\frac{{\ⅇ}^{-z}\left(1+z\right)}{z^2}$