Oh, that's really nifty. I first got embarassed by not knowing of that direct way here: http://gowers.wordpress.com/2008/07/30/recognising-countable-sets/ http

Oh, that's really nifty. I first got embarassed by not knowing of that direct way here: http://gowers.wordpress.com/2008/07/30/recognising-countable-sets/ http://gowers.wordpress.com/2008/07/30/recognising-countable...