@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix log:  <http://www.w3.org/2000/10/swap/log#> .
@prefix :     <http://example.org/#> .

:Socrates a :Greek .
:Aristotle a :Greek .

:Greek rdfs:subClassOf :Person .

{ ?x a :Greek . }
    => { ?x a :Person . } .