def find_judged_qrps(db_conn):
    """
    Find all the previously judged query-result pairs in the Arcs DB.

    Args:
        db_conn (psycopg2.extensions.connection): Connection to a database

    Returns:
        A set of query-result fxf pairs
    """
    query = "SELECT query, result_fxf FROM arcs_query_result WHERE judgment IS NOT NULL"

    with db_conn.cursor() as cur:
        cur.execute(query)
        return {(row[0], row[1]) for row in cur}