Re: Re: Checking for a given phrase in an expression

• To: mathgroup at smc.vnet.net
• Subject: [mg60800] Re: [mg60761] Re: [mg60744] Checking for a given phrase in an expression
• From: Andrzej Kozlowski <andrzej at yhc.att.ne.jp>
• Date: Thu, 29 Sep 2005 05:41:09 -0400 (EDT)
• References: <200509270745.DAA18926@smc.vnet.net> <200509280540.BAA08299@smc.vnet.net>
• Reply-to: Andrzej Kozlowski <andrzej at akikoz.net>
• Sender: owner-wri-mathgroup at wolfram.com

```It seems to be an undocumented feature that Subsets works with
expressions with heads other than List but what it seems to be based
on the following rule:

Subsets[f[a,b,c,....]]

is the same as

f@@@Subsets[{a,b,c,...}]

The OP never explained precisely what he meant by  "a phrase bb
exists in aa" so many different interpretations are possible but note
that with your approach a is not a "phrase" in a*b+c

aa=a*b+c;bb=a;

MemberQ[Subsets[aa, Length[bb]], bb]

False

while with the pattern matching based approach it is:

SubExpressionQ[a_, b_] := (a /. b -> Unique[]) =!= a

SubExpressionQ[aa,bb]

True

Of course it is all a matter of interpretation.

Andrzej Kozlowski

On 28 Sep 2005, at 14:40, <bsyehuda at gmail.com> <bsyehuda at gmail.com>
wrote:

>
> Out of the sleeve solution (I do not have time to have an
> intelligent one
> right now) is to generate subsets of aa and then test if bb is a an
> element
> in the list of subsets so
> MemberQ[Subsets[aa, Length[bb]], bb]
> returns True as expected
> yehuda
>
>
> On 9/27/05, lost.and.lonely.physicist at gmail.com <
> lost.and.lonely.physicist at gmail.com> wrote:
>
>>
>> Hello everyone
>>
>> Is it possible to ask Mathematica to check if a given phrase
>> occurs in
>> an expression? Say I have
>>
>> aa = 1 + x + x y + Log[Sin[z]]
>>
>> and
>>
>> bb = x + Log[Sin[z]]
>>
>> Can Mathematica tell me such a phrase bb exists in aa? Can it tell me
>> its 'position' within the expression aa?
>>
>> Thanks for the help!
>>
>>
>>
>
>
>

```

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