php 5.3 subclass singleton

for the "Late Static Bindings" imported by php from version 5.3,( http://php.net/manual/en/language.oop5.late-static-bindings.php)
singleton patterns:

<?php
class Singleton {

    static private $instance;
	
	protected static function create(){
		if(is_null(self::$instance)){
            self::$instance = new self();
        }
        return self::$instance;
	}
    static public function instance(){
	return static::create();   //!important to use static
		
    }

    public function __construct(){echo 1;}

}

class MySingleton extends Singleton {
	static private $instance;                //in subclass,explicitly declare this and the method below
	protected static function create(){
		if(is_null(self::$instance)){
            self::$instance = new self();
        }
        return self::$instance;
	}

}
class YourSingleton extends Singleton {
	static private $instance;
	protected static function create(){
		if(is_null(self::$instance)){
            self::$instance = new self();
        }
        return self::$instance;
	}
}
class ThirdSingleton extends MySingleton {
	static private $instance;
	protected static function create(){
		if(is_null(self::$instance)){
            self::$instance = new self();
        }
        return self::$instance;
	}
}
echo get_class(Singleton::instance());		//=>Singleton
echo get_class(MySingleton::instance());	//=> MySingleton
echo get_class(MySingleton::instance());	//=> MySingleton
echo get_class(YourSingleton::instance());	//=>YourSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton

a code-less but confusable style:

<?php
class Singleton {

    static private $instance;

    static public function instance(){
		static $instance = null;  //should not add self:: or static:: here 

        return $instance ?: $instance = new static;
    }

    public function __construct(){echo 1;}

}

class MySingleton extends Singleton {
}
class YourSingleton extends Singleton {
}
class ThirdSingleton extends MySingleton {
}
echo get_class(Singleton::instance());		//=>Singleton
echo get_class(MySingleton::instance());	//=> MySingleton
echo get_class(MySingleton::instance());	//=> MySingleton
echo get_class(YourSingleton::instance());	//=>YourSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton

the following maybe the best one:

class Singleton {

    static protected $instance;              //should not be private
	
    static public function instance(){
        if(is_null(static::$instance)){         //important to use static
            static::$instance = new static();
        }
        return static::$instance;

    }

    public function __construct(){echo 1;}

}

class MySingleton extends Singleton {
	static protected $instance;    //must explicitly declared
}
class YourSingleton extends Singleton {
	static protected $instance;	
}
class ThirdSingleton extends MySingleton {
	static protected $instance;	
}
echo get_class(Singleton::instance());		//=>Singleton
echo get_class(MySingleton::instance());	//=> MySingleton
echo get_class(MySingleton::instance());	//=> MySingleton
echo get_class(YourSingleton::instance());	//=>YourSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton
echo get_class(ThirdSingleton::instance()); //=>ThirdSingleton