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<?php

if ( ! function_exists( 'prefix_pingback_header' ) ) {
	/**
	 * Add a pingback url auto-discovery header for singularly identifiable articles.
	 */
	function prefix_pingback_header() {
		if ( is_singular() && pings_open() ) {
			printf( '<link rel="pingback" href="%s">' . "\n", get_bloginfo( 'pingback_url' ) );
		}
	}
	add_action( 'wp_head', 'prefix_pingback_header' );
}