       Re: algebraic substitution rules

• To: mathgroup at smc.vnet.net
• Subject: [mg30757] Re: algebraic substitution rules
• From: "Orestis Vantzos" <atelesforos at hotmail.com>
• Date: Sun, 9 Sep 2001 03:27:06 -0400 (EDT)
• Organization: National Technical University of Athens, Greece
• References: <9ncfq6\$pt5\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Well, Mathematica begins to apply the rules (oh, and never use
a_->Expand[a], always a:>Expand[a]) , so it looks at the whole expression
and finds that the pattern of the last rule is valid .... 1+x^2+x^3+x^4 is
an a_ so it expands it and returns exactly the same. Content, it stops there
(since only one rule is applied to each part of an expression).
Orestis

"Cattiaux Isabelle" <Isabelle.Cattiaux at univ-valenciennes.fr> wrote in
message news:9ncfq6\$pt5\$1 at smc.vnet.net...
>
> Hi,
>
>   Could someone tell me why the first substitution rule
>  works and the second doesn't
>
> In:==
> 1+x^2+x^3+x^4 /. {x^2->1+x ,x^3->x(1+x) ,x^4->(1+x)^2}
>
> Out==
> 2 + x + x(1 + x)+ (1 + x)^2
>
> In:==
> 1+x^2+x^3+x^4 /. {x^2->1+x ,x^3->x(1+x) ,x^4->(1+x)^2,a_->Expand[a]}
>
> Out==
> 1 + x^2 + x^3 + x^4
>
> --
> Isabelle Cattiaux-Huillard
> Universite de Valenciennes
>

```

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