<?php

class A {
    static protected function f() {return 'A::f()';}
}
class B1 extends A {
    static protected function f() {return 'B1::f()';}
}
class B2 extends A {
    static public function test() {
        var_dump(is_callable('B1::f'));
        B1::f();
    }
}
B2::test();

?>