Counterexamples

Hello,

in order not to forget them, I started collecting our precious 
counterexamples in a web page, at 
<http://alessio.guglielmi.name/res/cos/cex.html>.

I've put there all those I could find in my notes. In the process, I 
discovered many things which required a lot of work that I had 
completely forgotten!

If you have other counterexamples, please send them to me.

-Alessio