prefix :       <http://example.org/>
prefix xsd:    <http://www.w3.org/2001/XMLSchema#>

:ok_s :p "A", "B", "C", "S" .   # Should pass as S
:ok_b :p "A", "B" .             # Should pass as B
:ok_c :p "A", "C" .             # Should pass as C
:ko_a :p "A" .                  # Should fail as A because it is abstract
:ko_s :p "A", "B", "C" .        # Should fail as S because it has no "S"
