The simplify/@ function is used to simplify expressions which contain operators.

Specifically, it simplifies compositions of inverses.  It uses the table invfunc as its knowledge base for these simplifications, so that it is possible for the user to modify the action of this function.

simplify(sin@arcsin, `@`);

$\left(\right)\mapsto \mathrm{args}$

simplify(exp@ln, `@`);

$\left(\right)\mapsto \mathrm{args}$

invfunc[f] := g:

simplify(f@@(-1)@g@@2);

$g^{\left(3\right)}$