I want to add elements of the fraction field of QQ[x,y] to a set,
i.e., make sure there are no repeats.  However, set.add()ing an
element that is equal to a previous element sometimes puts another
copy of the element in.  Witness the following behavior:

> R = PolynomialRing(QQ,'x,y')
> K = R.fraction_field()
> x,y = gens(K)
> (2*x)/(2*y) == x/y

True

> x/y in set([(2*x)/(2*y)])

False

> x/y in [(2*x)/(2*y)]

True

Why should these last two behaviors differ?  And how do I get the
second behavior out of a set without converting to a list and back?
For example, is there some way to force elements of K into a canonical
form?

Thanks,
Josh

WinXP/VMware Player
SAGE Version 2.10.3, Release Date: 2008-03-11
Acquired via binary build


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