Re: algebraic ReplaceAll?

*To*: mathgroup at smc.vnet.net*Subject*: [mg122351] Re: algebraic ReplaceAll?*From*: Shizu <slivo.vitz at msa.hinet.net>*Date*: Wed, 26 Oct 2011 17:38:14 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Replacement (â??term rewriting) in Mathematica works with FullForm[] of expressions. It takes account of associativity and commutativity, though. Just like that Mathematica cannot see that Rational is Real, it works with forms, but not mathematical meaning. You could expand Mathematica by saying something like: -x + w /. {x - w -> y, -(x - w) -> -y} But then, is Mathematica a CAS or AI system? The system is based on rewriting, not thinking. Correctness is more important than smartness in a CAS. It's possible that in the future, Mathematica could talks with you and figure out what you really want.