allow_subdirectory_install()

function allow_subdirectory_install() {
	global $wpdb;
        /**
         * Filters whether to enable the subdirectory installation feature in Multisite.
         *
         * @since WP-3.0.0
         *
         * @param bool $allow Whether to enable the subdirectory installation feature in Multisite. Default is false.
         */
	if ( apply_filters( 'allow_subdirectory_install', false ) )
		return true;

	if ( defined( 'ALLOW_SUBDIRECTORY_INSTALL' ) && ALLOW_SUBDIRECTORY_INSTALL )
		return true;

	$post = $wpdb->get_row( "SELECT ID FROM $wpdb->posts WHERE post_date < DATE_SUB(NOW(), INTERVAL 1 MONTH) AND post_status = 'publish'" );
	if ( empty( $post ) )
		return true;

	return false;
}