Hello everybody,

Looking at the combinatorial functions page (http://www.sagemath.org/
doc/reference/sage/combinat/combinat.html), I see that there exists a
union function, but no intersection function?

This would be useful to find the probability of joint sets.

Also, I found after a few hours of searching everywhere that the union
function would only work alright when the type of class used is of the
'set_object_enumerated_with_category' type.

For example, doing:
S1 = Permutations(2).union(Permutations(2)); S1.list() # will produce
something like:
-> [[1, 2], [2, 1], [1, 2], [2, 1]]

To get a correct result (without repeated identical results), one
needs to force the correct "enumerated with category" type using:
S2 = Set(Permutations(2)).union(Set(Permutations(2))); S2.list() #
will produce the correct result
-> [[1, 2], [2, 1]]

Maybe this could be documented somewhere... If it already is, I
couldn't find it.

Thanks,

Maxim

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