Services & ResourcesWolfram ForumsMathGroup Archive

[Date Index] [Thread Index] [Author Index]

Re: To be or not to be...

• To: mathgroup at smc.vnet.net
• Subject: [mg62032] Re: To be or not to be...
• From: dh <dh at metrohm.ch>
• Date: Wed, 9 Nov 2005 05:05:51 -0500 (EST)
• References: <dksd37$h58$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi Ingolf,
the problem is not with Sequence, but with Equal and its brethren. 
Sequence will simply insert an empty list into these functions.
We then have:

Equal[]
Unequal[]
SameQ[]
UnsameQ[]

the amazing fact is that all these are giving True.

The closet thing one finds in the Help is:

"Equal[e] gives True."

and similar for the other functions.
Here e  means an expression. To make ends meet, one has to assume that 
"expression" in this context"  can also mean "nothing" or no arguments. 
The amazing thing here is, that in general, a pattern of f[x_] does not 
fit f[]. Why should Equal be an exception???

sincerely, Daniel

Ingolf Dahl wrote:
> To Mathgroup,
> 
> Try the following commands in order:
> 
> b = Sequence[]
> 
> b == Sequence[]
> 
> b != Sequence[]
> 
> b === Sequence[]
> 
> b =!= Sequence[]
> 
> The four last lines all evaluate to "True" for me. Quite amazing!
> 
> Best regards
> 
> Ingolf Dahl
> 
> Sweden
> 
> 
> 

• Follow-Ups:
  • Re: Re: To be or not to be...
    • From: Pratik Desai <pdesai1@umbc.edu>