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Re: Peculiar output from Union ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg108509] Re: Peculiar output from Union ?
  • From: rafscipio <scipionedalferro at yahoo.it>
  • Date: Sun, 21 Mar 2010 02:05:19 -0500 (EST)
  • References: <ho1ui0$hov$1@smc.vnet.net>

On 20 Mar, 08:47, Jack L Goldberg 1 <jackg... at umich.edu> wrote:
> Hi Folks,
>
> Can anyone explain this:
>
> In[1]:= Union[  1 < x < 2, 3 < x < 5  ]
>
> Out[1]= 5 < x
>
> ??
>
> I am using a MacBook Pro, OS 10.6.2
>
> Thanks,
>
> Jack

Hi,

As u can read on help of Union function in Generalization and
Extension par., "Union works with any head, not just List":

In[1]:= Union[f[a, x, b], f[c, x, d]]

Out[1]= f[a, b, c, d, x]

In your case, considering the internal representation of the
expressions, it results:

In[2]:= 1 < x < 2 // FullForm
Out[2]//FullForm= Less[1,x,2]

In[3]:= 3 < x < 5 // FullForm
Out[3]//FullForm= Less[3,x,5]

Hence using formula  [1] the result of your union is equivalent to:

Less[1,2,3,5,x]

...and it's equivalent to 1<2<3<5<x
...and so to to 5<x

Scipione


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