  A modified definition of the category of forests by Costello and expounded
upon by Getzler is given. This language is used to prove some cofibration
properties of the W construction for colored operads, following the work of
Berger-Moerdijk. An application is given to the swiss cheese operad. The
language of forests is convenient for showing that the swiss cheese operad is
equivalent to its free degree 0 and 1 pieces.
