# Combinatorial elements and classes

I would like to construct a free module over QQ (for simplicity) whose basis is index by finite sequences of strictly decreasing positive half odd integers (so odd numbers divided by 2).

`CombinatorialFreeModule()`

seems like the tool to use for this, if I can define the class of sequences mentioned in the previous sentence. I understand that these sequences are in bijection with integer partitions, so I could just use `Partitions()`

as in `CombinatorialFreeModule(QQ,Partitions())`

. However, I'm trying to improve my understanding of Sage and so I'm trying to program an appropriate class of sequences of half odd integers by looking at the source code for `Partitions()`

.

Sadly, I'm running into trouble before I even managed to get started properly. I think my class will need to inherit from `CombinatorialElement`

which the `Partitions()`

source code imports via
`from .combinat import CombinatorialElement`

.
This produces the following error:
`Import Error: attempted relative import with no known parent package`

.

So how do I import CombinatorialElement properly?