Re: To be or not to be...

*To*: mathgroup at smc.vnet.net*Subject*: [mg62039] Re: [mg62002] To be or not to be...*From*: Kristjan Kannike <kkannike at physic.ut.ee>*Date*: Wed, 9 Nov 2005 05:06:03 -0500 (EST)*References*: <200511090845.DAA17323@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On Wed, 9 Nov 2005, Ingolf Dahl wrote: > 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! There is really nothing mysterious. The FullForm of e.g. b==Sequence[] would be Equal[b, Sequence[]]. As an empty sequence is spliced into the argument list of Equal, the expression is equivalent to Equal[b] that is _defined_ to be True (check the Help). Similarly for != or UnEqual. Try a==Sequence[] for an undefined a, and it evaluates to True as well. Kristjan Kannike <http://www.physic.ut.ee/~kkannike/>

**References**:**To be or not to be...***From:*"Ingolf Dahl" <ingolf.dahl@telia.com>