This routine is part of the liesymm package and is loaded via with(liesymm).

Given an expression involving Diff or diff, expr reorder the partials to an ``address'' ordering so that mixed partials can be recognized as equivalent.

$\mathrm{with}\left(\mathrm{liesymm}\right)\:$$\mathrm{setup}\left(x\,y\,z\right)\:$

$\mathrm{mixpar}\left(\mathrm{Diff}\left(f\left(x\,y\right)\,x\,y\right)\right)$

$\frac{{\partial }^2}{\partial x\partial y}f\left(x\,y\right)$

$\mathrm{mixpar}\left(\mathrm{Diff}\left(\mathrm{Diff}\left(f\left(x\,y\right)\,x\right)\,y\right)\right)$

$\frac{{\partial }^2}{\partial x\partial y}f\left(x\,y\right)$

$\mathrm{mixpar}\left(\mathrm{Diff}\left(\mathrm{Diff}\left(f\left(x\,y\right)\,y\right)\,x\right)\right)$

$\frac{{\partial }^2}{\partial x\partial y}f\left(x\,y\right)$