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Re: Head logic

• To: mathgroup at smc.vnet.net
• Subject: [mg97050] Re: [mg97033] Head logic
• From: Sseziwa Mukasa <mukasa at jeol.com>
• Date: Wed, 4 Mar 2009 07:09:55 -0500 (EST)
• References: <200903031055.FAA02912@smc.vnet.net>

On Mar 3, 2009, at 5:55 AM, 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?
>

== only evaluates to False for comparisons between certain types of  
raw data according to the help documentation, == apparently doesn't  
evaluate to False for Symbols of different value.  You can use ===  
and =!= if this is a problem.

Regards,

Sseziwa

• References:
  • Head logic
    • From: carlos@colorado.edu