Re: ((a&&b)||c)==((a||c)&&(b||c)) is not true
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- Subject: [mg62086] Re: ((a&&b)||c)==((a||c)&&(b||c)) is not true
- From: "Steven T. Hatton" <hattons at globalsymmetry.com>
- Date: Fri, 11 Nov 2005 02:51:49 -0500 (EST)
- References: <200511090845.DAA17387@smc.vnet.net> <dksig6$k6l$1@smc.vnet.net> <dkuvog$7rc$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Richard Fateman wrote: > A good reason for Mathematica to fail to show that these > are the same, is that they are in some senses different. > > > These look like logical statements and as such they look like they > are logically identical, but these are actually > programs with short-circuit evaluation. > > > Consider > c[] := (Print[C_called]; True) > a[] := (Print[A_called]; False) > b[] := (Print[B_called]; True) > (a[] && b[]) || c[] > (a[] || c[]) && (b[] || c[]) > > They are different PROGRAMS. Good observation. There should, however, be some way to tell Mathematica to treat them as traditional symbolic logic statements. I don't believe that LogicExpand will do that for me. I'm not sure what happens with Implies, but my observation is that it does not handle all cases. -- The Mathematica Wiki: http://www.mathematica-users.org/ Math for Comp Sci http://www.ifi.unizh.ch/math/bmwcs/master.html Math for the WWW: http://www.w3.org/Math/
- References:
- ((a&&b)||c)==((a||c)&&(b||c))
- From: "Steven T. Hatton" <hattons@globalsymmetry.com>
- ((a&&b)||c)==((a||c)&&(b||c))