Thanks for all your kind wishes and suggestions about my trapped cat. Without seeing the bookcase, it was hard appreciate the situation. The cat was trapped underneath, in a small space beneath the bottom shelf, a very large and heavy bookcase (10 feet tall, 8 feet wide, substantial enough to be loaded with what I estimate were at least 500 lbs of books). The cat did not have enough space to stand up, and apparently could not get a purchase to push himself out, nor could he get his head and both front paws out to pull himself free either. A complicating factor was that the top sections of the bookcase were cabled to the wall to prevent them from tipping forward and causing all sorts of carnage.
Reader bob via a long discussion over e-mail, recommended the solution my building handymen also suggested when then came up to have a look: pivoting the bookcase out an inch or so. Bob insisted I empty the bookcase and get the guys to use a metal rod as a lever and a piece of wood to protect the bookcase, both of which were good calls, since two men were barely able to budge it even using the rod to amplify force. The cat popped out almost immediately. They building staff shoved the bookcase back, with the result that the space behind it is tighter before and I can’t see how he can possibly get back there now.
Thanks again for your patience and kind wishes! Aside from being very dirty, the cat seems none the worse for wear.