SPARQL Query Puzzler

Dear List Members,

I am stuck with formulating a SPARQL query which checks wheter one graph
structure is contained in another.
Consider the following example of an imaginery "theory-of-sets" ontology:

setA a Set
setB a Set
setC a Set
setD a Set

el_1 a Element
el_2 a Element
el_3 a Element
el_4 a Element

setA contains el_1, el_2, el_3
setB contains el_1, el_3
setC contains el_2, el_4
setD contains el_3

Now here is the question: Is it possible (with a SPARQL query) to retrieve
all sets, which are sub-sets of setA?
To be more precise: Is there a SPARQL query, which returns all Sets
containing only Elements, which are also contained in setA?

Premise: you know the Elements of setA explicitly, but you know nothing
about the other Sets and their Elements.

Here's my try (Problem: it doesn't filter out setC):
SELECT ?set
WHERE {
        ?set a :Set .
        ?set :contains ?x .
        FILTER (?x = :Element_1 || ?x = :Element_2 || ?x = :Element_3 )
}


The obvious solution would be setB and setD (and maybe setA itself, too),
but not setC.
I have tried to solve this puzzle for days now, without success. I wonder if
such a query is possible with SPARQL.

Any suggestions are welcome!

Best regards,
Torben