Get MAX result from COUNT in SPARQL - sparql

Question

I have this query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX curricula: <http://www.semanticweb.org/lsarni/ontologies/curricula#>
SELECT ?topic (COUNT(?x) as ?number_of_courses)
WHERE {
?topic curricula:taughtIn ?x .
}
GROUP BY ?topic
ORDER BY desc(?number_of_courses)
That returns:
Now I want to get the ?topic with the max ?number_of_courses, in this case Engineering
I managed to get the max ?number_of_courses with this query (following this answer):
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX curricula: <http://www.semanticweb.org/lsarni/ontologies/curricula#>
SELECT (MAX(?number_of_courses) AS ?maxc)
WHERE{
{
SELECT ?topic (COUNT(?x) as ?number_of_courses)
WHERE {
?topic curricula:taughtIn ?x .
}
GROUP BY ?topic
}
}
This returns:
But I can't manage to get the ?topic.
How could I fix this?
Update
I tried what I understood from AKSW comment:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX curricula: <http://www.semanticweb.org/lsarni/ontologies/curricula#>
SELECT ?topic
WHERE {
?topic curricula:taughtIn ?x .
{
SELECT (MAX(?number_of_courses) AS ?max)
WHERE {
{
SELECT ?topic (COUNT(?x) as ?number_of_courses)
WHERE {
?topic curricula:taughtIn ?x .
}
GROUP BY ?topic
}
}
}
}
GROUP BY ?topic
HAVING (COUNT(?x) = ?max)
But it returns nothing.
Example
For this minimal example the result should be Topic_2 since it's taughtIn two courses.
#prefix : <http://www.semanticweb.org/lsarni/ontologies/curricula#> .
#prefix owl: <http://www.w3.org/2002/07/owl#> .
#prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
#prefix xml: <http://www.w3.org/XML/1998/namespace> .
#prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
#prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
#base <http://www.semanticweb.org/lsarni/ontologies/curricula> .
<http://www.semanticweb.org/lsarni/ontologies/curricula> rdf:type owl:Ontology .
#################################################################
# Object Properties
#################################################################
### http://www.semanticweb.org/lsarni/ontologies/curricula#taughtIn
:taughtIn rdf:type owl:ObjectProperty ;
rdfs:subPropertyOf owl:topObjectProperty .
### http://www.w3.org/2002/07/owl#topObjectProperty
owl:topObjectProperty rdfs:domain :Topic ;
rdfs:range :Course .
#################################################################
# Classes
#################################################################
### http://www.semanticweb.org/lsarni/ontologies/curricula#Course
:Course rdf:type owl:Class ;
owl:disjointWith :Topic .
### http://www.semanticweb.org/lsarni/ontologies/curricula#Topic
:Topic rdf:type owl:Class .
#################################################################
# Individuals
#################################################################
### http://www.semanticweb.org/lsarni/ontologies/curricula#Course_1
:Course_1 rdf:type owl:NamedIndividual ,
:Course .
### http://www.semanticweb.org/lsarni/ontologies/curricula#Course_2
:Course_2 rdf:type owl:NamedIndividual ,
:Course .
### http://www.semanticweb.org/lsarni/ontologies/curricula#Topic_1
:Topic_1 rdf:type owl:NamedIndividual ,
:Topic ;
:taughtIn :Course_1 .
### http://www.semanticweb.org/lsarni/ontologies/curricula#Topic_2
:Topic_2 rdf:type owl:NamedIndividual ,
:Topic ;
:taughtIn :Course_1 ,
:Course_2 .
### Generated by the OWL API (version 4.2.8.20170104-2310) https://github.com/owlcs/owlapi