The first elaboration says that when Pat finds the room stuffy he unblocks vent2. We have
or, more elaborately,
(24) remains the same except that perhaps we should change the notation so that instead of S3 and S3' we write S2'' and S2''', since these are now intermediate situations. The situation S4 is now unstable.
Now let's add a second elaboration in which Mike finds the room cold when there is an unblocked vent and blocks vent2. It is expressed by adding
With both of these elaborations, we get an oscillation; Pat unblocks
vent2 and Mike blocks it again. 
and 
are no longer
defined.
