[Tree terminology]

Brendan McKay bdm at cs.anu.edu.au
Thu Sep 19 15:38:20 CEST 2002

* Christian G.  Bower <bowerc at usa.net> [020919 09:28]:
> Antti Karttunen <karttu at megabaud.fi> wrote:
> ...
> Plane and planar are synonyms, but oriented usually means that the edges
> have arrow on them as in a digraph. (Although I can't be sure how your
> reference uses the term.)

I'm answering in reference to accepted terminology, not wrt particular
sequences.  There is no universal agreement about the meanings of
these words, but the most common usage is:

planar = ABLE TO BE drawn in the plane without crossings
plane = ACTUALLY drawn in the plane without crossings

The difference between these two is critical when counting things
since one object might be drawable in multiple distinct ways.
(However, there are further options when defining the equivalence
of drawings such as whether mirror images are equivalent.)

Many authors use "oriented graph" to mean a simple undirected
graph which has a direction associated with each edge.  This is
not the same as "digraph" because it does not allow edges x->y
and y->x to be present simultaneously.

In both cases, descriptions in the database should only be
changed after careful consideration.


More information about the SeqFan mailing list