Recursive axioms in OWL DL

Hi,

I just wanted to know whether the constraint

   "All axioms must be well-formed, with no missing or
    extra components, and must form a tree-like structure"
   (OWL Web Ontology Language Reference, sec. 8.2)

implies that the TBox of an OWL DL application
(seen as a Description Logic) must NOT be cyclic.

Thanks in advance,
Andrea