Esty: Get dies with only one occurrence d1 for coin type

esty_d1.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 (count(?die) as ?dieCount) WHERE {
  {
    SELECT DISTINCT ?die (count(?object) as ?count)  WHERE {
        ?object nmo:hasTypeSeriesItem <http://numismatics.org/crro/id/rrc-336.1c> .
        GRAPH <http://nomisma.org/editor/rschaefer> {
          ?object nmo:hasObverse/nmo:hasDie/rdf:value ?die 
        }
    } GROUP BY ?die HAVING (?count = 1)
  }
}