revision ranges

[Gilles Moris]

On Fri November 21 2008 12:47:08 Benoit Boissinot wrote:
> > BEGIN:END denotes the revisions which are greater than or equal to BEGIN
> > and less than or equal to END.
> >
> > But how this "A greater than B" defined? Does it mean that B is a
> > descendant of A or just that B has higher revision number than B?
> 
> Higher revision number (as shown by hg log). You can get more precise ranges
> with the parentspec extension (I think Matt is not opposed to a similar
> feature in core hg).
> 

OK, but doesn't it give more information though.
As I understand from http://en.wikipedia.org/wiki/Directed_acyclic_graph 
a DAG will give rise to a partial ordering, so my understanding is that:

if you have two HG rev numbers A and B such that a A > B, then
- A can NOT be an ascendant of B, though it can be a descendant
- B can NOT be a descendant of A, though it can be an ascendant

Am I right ?

Thanks.
Gilles.