From: Rick DeNatale Date: 2008-07-03T20:48:57+09:00 Subject: Re: Ranges and Enumerable problems ------=_Part_6562_22876881.1215085925285 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline On Thu, Jul 3, 2008 at 5:23 AM, Robert Klemme wrote: > 2008/7/3 Todd Benson : > > On Wed, Jul 2, 2008 at 5:07 PM, Todd Benson wrote: > >> On Wed, Jul 2, 2008 at 3:50 PM, Rick DeNatale > wrote: > >>> !(for all s: (s <=>s.succ) == -1) > >> > >> Well, not really. That gives you no information as to whether such a > >> thing does exist. That statement would be true, but not definitive, > >> meaning, that it would be true if there is _no_ s that satisfies. > > > > Okay, that may have been a major faux pas on my part :-) > > It is. :-) not (for all e: X(e)) <=> (there is at least one e: not X(e)) > > Yep, I remember getting A's in my logic courses. I vaguely remembered this as being related to De Morgan's laws in Boolean algebra, and Wikipedia seems to agree http://en.wikipedia.org/wiki/De_Morgan%27s_laws#Further_explanation -- Rick DeNatale My blog on Ruby http://talklikeaduck.denhaven2.com/ ------=_Part_6562_22876881.1215085925285--