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MathGroup Archive 2005

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Re: Re: Free variables in an expression

  • To: mathgroup at
  • Subject: [mg54828] Re: [mg54794] Re: [mg54758] Free variables in an expression
  • From: Andrzej Kozlowski <akoz at>
  • Date: Wed, 2 Mar 2005 22:29:17 -0500 (EST)
  • References: <>
  • Sender: owner-wri-mathgroup at

The problem is that the OP completely failed to explain the meaning of  
"free" and "bound". With the usual meaning of these terms in  logic the  
following sentence:

expr=Exists[y, Element[y, Reals], x*y - 1 == 0]

contains just one free variable x.  In this case however

Cases[expr, _Symbol?( !NumericQ[#1] & ), Infinity]

{y, y, Reals, y, x}

which is of course wrong. However,



returns the correct answer.

I have to admit I rather doubt that this is what the OP meant, but if  
not than his use of "free" and "bound" is non-standard.

Andrzej Kozlowski

On 2 Mar 2005, at 07:26, Bob Hanlon wrote:

> expr=Log[6x]+y/3-Exp[z]*Pi-3*I;
> Cases[expr, _Symbol?(!NumericQ[#]&),Infinity]
> {z,y,x}
> Bob Hanlon
>> From: Sascha Kratky <notvalid at>
To: mathgroup at
>> Date: 2005/03/01 Tue AM 01:58:13 EST
>> Subject: [mg54828] [mg54794] [mg54758] Free variables in an expression
>> Is there a Mathematica built-in function that gives a list of free
>> (unbound) variables in an arbitrary expression?
>> Thanks,
>> Sascha

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