       Re: algebraic substitution rules

• To: mathgroup at smc.vnet.net
• Subject: [mg30743] Re: algebraic substitution rules
• From: bghiggins at ucdavis.edu (Brian Higgins)
• Date: Sun, 9 Sep 2001 03:26:36 -0400 (EDT)
• References: <9ncfq6\$pt5\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```You want to apply the last rule a_->Expand[a], after  you have applied
all the other rules. Thus

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=3 + 4*x + 2*x^2

Brian

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

```

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