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Re; Tally[ ] and Union[ ]

• To: mathgroup at smc.vnet.net
• Subject: [mg83398] Re; Tally[ ] and Union[ ]
• From: Thomas E Burton <tburton at brahea.com>
• Date: Mon, 19 Nov 2007 06:18:39 -0500 (EST)

I immediately suspected Combinatorica`IsomorphicQ. I was able to  
convince myself, however, that IsomorphicQ is symmetric and  
transitive over the set of 21 graphs produced by diagrams[3]. Do we  
ask any more of a test for equivalence? If not, then suspicion  
reverts to Tally, which is yielding too many results. I've no answer.

> "A sorted  Tally is equivalent to a list of counts for the  Union:"
>
> This is what I indeed expect of Tally and Union, in particular then  
> it holds for any list: Length[Tally[list]]    is equal to     Length 
> [Union[list]].