.
Formula
is true because it is the conjunction of
and
.
![[Graphics:submitted.nbgr88.gif]](submitted.nbgr88.gif)
![[Graphics:submitted.nbgr89.gif]](submitted.nbgr89.gif)
. .![[Graphics:submitted.nbgr90.gif]](submitted.nbgr90.gif)
is true because it is the conjunction of![[Graphics:submitted.nbgr91.gif]](submitted.nbgr91.gif)
and ![[Graphics:submitted.nbgr92.gif]](submitted.nbgr92.gif)
.