On Jul 23, 2012, at 12:33 PM, Sergiu Ivanov <[email protected]> wrote:

> On Mon, Jul 23, 2012 at 9:17 PM, Aaron Meurer <[email protected]> wrote:
>> On Jul 23, 2012, at 2:20 AM, Sergiu Ivanov <[email protected]> 
>> wrote:
>>
>>> On Sun, Jul 22, 2012 at 11:44 PM, Aaron Meurer <[email protected]> wrote:
>>>>
>>>> Can you be more specific?  Most likely, one of the results is "better"
>>>> than the other, and the algorithm should be fixed to always give it
>>>> regardless of ordering.
>>>
>>> FiniteSet._complement works as follows:
>>>
>>>>>> from sympy import FiniteSet
>>>>>> FiniteSet(1, 2, 3).complement
>>> (-oo, 1) U (1, 2) U (2, 3) U (3, oo)
>>>
>>> I'm not sure this result can be achieved more efficiently by a
>>> different approach then sorting the elements.
>>
>> This is the exact same as FiniteSet itself. Union's args do not need
>> to be sorted except within the printer.
>
> I was referring to the fact that, for example, FiniteSet(3, 1,
> 2).complement should return the same result.
>
> In other words, to get the complement relative to RR, one has to sort
> the numbers in the FiniteSet first, because otherwise one may get
> stuff like (-oo, 3) U (1, 2) U (2, oo).

Well this answer is simply wrong.

Aaron Meurer

>
> I really hope my explanation is more or less clear.
>
> Sergiu
>
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