public static function find(array $ar, array $where){
    //die(var_dump($where));
    if ( !empty($where) ){
      foreach ( $ar as $i => $v ){
        $ok = 1;
        foreach ( $where as $k => $w ){
          if ( !isset($v[$k]) || ($v[$k] !== $w) ){
            $ok = false;
            break;
          }
        }
        if ( $ok ){
          return $i;
        }
      }
    }
    return false;
  }