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 *S*3 and *S*3' we write
*S*2'' and *S*2''', since these are now intermediate situations.
The situation *S*4 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.

Fri Feb 8 17:29:20 PST 2002