The combine function is applied to the arguments of a piecewise function.

To make a single piecewise expression out of two, use convert(expr, piecewise, var).

$\mathrm{combine}\left(\mathrm{piecewise}\left(0<x\&comma;{\cos \left(x\right)}^2+{\sin \left(x\right)}^2\&comma;{\left(\exp \left(x\right)\right)}^2\exp \left(y\right)\right)\right)$

$\left\{\begin{array}{cc}{\&ExponentialE;}^{2x+y}& x\le 0\\ 1& 0<x\end{array}\right.$

$\mathrm{combine}\left(\mathrm{piecewise}\left(x<1\&comma;\exp \left(x\right)\exp \left(-2x\right)\&comma;3<x\&comma;4{\sin \left(x\right)}^3\right)\right)$

$\left\{\begin{array}{cc}{\&ExponentialE;}^{-x}& x<1\\ 0& x\le 3\\ -\sin \left(3x\right)+3\sin \left(x\right)& 3<x\end{array}\right.$