SELECT
  (tracker:uri-is-descendant ('file:///', 'file:///a') AS ?a)
  (tracker:uri-is-descendant ('file:///a', 'file:///b') AS ?b)
  (tracker:uri-is-descendant ('file:///a', 'file:///') AS ?c)
  (tracker:uri-is-descendant ('file:///', 'file:///a/b') AS ?d)
{
}