On Sat, Nov 09, 2013 at 11:04:47AM -0800, Christopher Smith wrote:
>  > +    This is because the two are not equal to each other in general.
>  > +    For example, consider `x == -1`:
>  > +
>  > +    >>> cbrt(x**3).subs(x, -1).expand(complex=True)
>  > +    1/2 + sqrt(3)*I/2
>  > +    >>> x.subs(x, -1)
> 
>    Ahh...well it could be said more directly in both places as
>    >> x = -1 >> sqrt(x**2) == x
>    False

This is a tautology.  See quoted above text.

>    >> sqrt(x**2).subs(x, -1) == -1 # x**2 is 1 so sqrt(1) is 1
>    False

Even worse.  There is a comment in the docstring.