On Wed, Nov 20, 2013 at 12:52:43AM -0800, Julien Rioux wrote:
>    In sympy/series/order.py:
> 
>  >
>  >      The formal definition for the order of a function `g(x)` about a point `a`
>  >      is such that `g(x) = O(f(x))` as `x \rightarrow a` if and only if for any
>  >      `\delta > 0` there exists a `M > 0` such that `|g(x)| \leq M|f(x)|` for
>  >      `|x-a| < \delta`. This is equivalent to `\lim_{x \rightarrow a}
>  > -    |g(x)/f(x)| < \infty`.
>  > +    \sup |g(x)/f(x)| < \infty`.
> 
>    The standard definition of big-O involves a limit superior, but our
>    implementation uses a limit.

I don't sure, why do you think so?  I think we can just return None in
the contains method (or is this already done for that case?) if limit
raises or return an unevaluated expression.

Anyway, we have to fix the formal definition (either the epsilon-delta
one or the "lim" one).