Como resolve herança multipla em PHP com interface?

Olá Caros,

Uma pergunta, herança múltipla em PHP se resolve assim? Qual seria a utilidade da interface neste caso, observando que sem a interface, o código tem o mesmo resultado.

?

interface iProfessor
{

public function teach();
}

interface iStudent
{

public function study();
}

class Person
{

private $identification;

public function getId()

{

return $this->identification;
}
public function setId($id)

{

$this->identification = $id;
}
}

class Professor extends Person implements iProfessor
{

private $salary;
public function getSalary()

{

return $this->salary;
}
public function setSalary($salary)

{

$this->salary = $salary;
}
public function teach()

{

return "teaching...";
}
}

class Student extends Person implements iStudent
{

private $subject;

public function study()

{

return "Studying...";
}
}

class ProfessorStudent
{

public $prof;
public $student;

public function getProfessorStudentDetails(Professor $prof, Student $student)

{

$studying = $student->study();
$teaching = $prof->teach();

$greetings = "I'm ".$teaching." and ".$studying.". my ID is ". $prof->getId(); ;

return $greetings;
}
}

$prof = new Professor();
$prof->setId(1);

$student = new Student();

$profStudent = new ProfessorStudent();

echo $profStudent->getProfessorStudentDetails($prof, $student);