Get reverse dies paired with an obverse die, and then get the obverse dies paired with those reverse dies.

die_pairings.sparql

PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX nm: <http://nomisma.org/id/>
PREFIX nmo: <http://nomisma.org/ontology#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

SELECT DISTINCT ?die ?dieLabel ?altDie ?altDieLabel (count(?object) as ?count)  WHERE {
  	BIND (<http://numismatics.org/rrdp/id/rrc-15.1.o.1> as ?die)
    GRAPH <http://nomisma.org/editor/rschaefer> {
      ?object nmo:hasObverse/nmo:hasDie/rdf:value ?die
      {
       	SELECT ?object ?altDie WHERE {
        	?object nmo:hasReverse/nmo:hasDie/rdf:value ?altDie
        }
      }
    }
    ?die skos:prefLabel ?dieLabel FILTER langMatches(lang(?dieLabel), "en").
    ?altDie skos:prefLabel ?altDieLabel FILTER langMatches(lang(?altDieLabel), "en").
} GROUP BY ?die ?dieLabel ?altDie ?altDieLabel ORDER BY ?dieLabel ?altDieLabel