Howard, you are right ...my solution lacks generality. Thanks
for pointing that out.
Roland, your solution is wonderful ! I didn't know about this option
It is funny that Roland's endorsement shows up after mine on your
computer Howard, since I posted slightly after him (according to the
time shown). Similarly on my PC, my solution shows up as the last
message (11th message) even though I posted it long before Howard's and
Roland's last comments !!!