PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX : <http://purl.org/net/schemarama#>
CONSTRUCT
{
  [] a :Error;
    :message 'Concept [1] is involved in a circularity in the generalisation hierarchy.';
    :implicated ( ?x );
  .
}
WHERE
{
  ?x skos:broader ?x.
}