define/linear sets up a definition of L which allows simplification and evaluation.

The properties of a linear operator are:

$\mathrm{define}\left(L\,'\mathrm{linear}'\right)$

$L\left(5\right)$

$5L\left(1\right)$

$L\left(3x+z\right)$

$3L\left(x\right)+L\left(z\right)$

$L\left(\mathrm{\pi }\right)$

$L\left(\mathrm{\pi }\right)$