SPARQL query with negation using ARQ in Jena

[Ondrej Zamazal]

Hi,
I am using ARQ in Jena and I am trying to figure out how I could query 
that a certain triple does not exist in the graph (negation as failure).

I found the document [1] where UNSAID operator is mentioned but it seems 
that this is not supported by ARQ. Right? There is also mentioned that 
combination of OPTIONAL and FILTER could work for some cases.  But I 
think that this is not sufficient for my case because there are not 
unbounded variables in my query, please see below.

In the query I would need to ask whether the specific triple is missing 
in a graph, e.g.

SELECT *
WHERE {
UNSAID { <http://ontology1#Concept1> rdfs:subClassOf 
<http://ontology1#Concept2> }.
}

I think UNSAID should be good for this case or maybe something like 'not 
ASK'. I would just need yes/no answer from query engine.

Would this be somehow possible?

Thank you for your reply in advance
Regards,
Ondrej