.
Formula
is true because it is the conjunction of
and
.
![[Graphics:submitted.nbgr77.gif]](submitted.nbgr77.gif)
![[Graphics:submitted.nbgr78.gif]](submitted.nbgr78.gif)
. .![[Graphics:submitted.nbgr79.gif]](submitted.nbgr79.gif)
is true because it is the conjunction of![[Graphics:submitted.nbgr80.gif]](submitted.nbgr80.gif)
and ![[Graphics:submitted.nbgr81.gif]](submitted.nbgr81.gif)
.