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Re: Head logic

• To: mathgroup at smc.vnet.net
• Subject: [mg97058] Re: Head logic
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Wed, 4 Mar 2009 07:12:00 -0500 (EST)
• References: <goj2bk$2qu$1@smc.vnet.net>

Hi,

may be there is a reason why there exist SameQ[]
(===) and UnsameQ[] (=!=).

The reason is that
a==b is may be true if a and b have values but general
this is an equation. If want to test something that
must yield True or False use SameQ[] anf UnsameQ[]

Regards
   Jens

carlos at colorado.edu wrote:
> Entering
> 
>    ClearAll[r];
>    Head[r]
>    Head[r]!=Symbol
>    Head[r]==Symbol
> 
> give Symbol, False and True as expected. But
> 
>    Head[r]==Integer
> 
> evaluates to Symbol==Integer. Why not False?
> Head[r] is certainly not Integer. Likewise
> 
>   r=4;
>   Head[r]==Integer
>   Head[r]!=Symbol
>   Head[r]==Symbol
> 
> give True (correct) but  Integer!=Symbol and Integer==Symbol.
> Why not True and False?
>