MathPHP\SetTheory\Set::isNotMember PHP Метод

    public function isNotMember($x) : bool
    {
        return !array_key_exists($this->getKey($x), $this->A);
    }

 /**
  * @dataProvider dataProviderForSingleSet
  */
 public function testIsNotMember(array $members)
 {
     $set = new Set($members);
     $this->assertTrue($set->isNotMember('TotallNotAMember'));
     $this->assertTrue($set->isNotMember('99999123'));
     $this->assertTrue($set->isNotMember(99999123));
 }