Is a blank node allowed as verb?

Hi,

Still debugging the Prolog SPARQL parser ...  I'm stuck with 
syntax-bnodes-04.rq:

PREFIX : <http://example.org/ns#>
SELECT * WHERE { :x _:a :q }

Using production [34], the _:a must match a Verb, but Verb [36] is only
VarOrIRIref | 'a'.  Verb doesn't appear to include blank node.

I guess I'm missing something, but I did look twice with a good break
in between :-)  Who can enlight me?

	Thanks --- Jan