themes-wordpress/publication/index.php

<?php
/**
 * The main template file.
 *
 * This is the most generic template file in a WordPress theme
 * and one of the two required files for a theme (the other being style.css).
 * It is used to display a page when nothing more specific matches a query.
 * E.g., it puts together the home page when no home.php file exists.
 * Learn more: http://codex.wordpress.org/Template_Hierarchy
 *
 * @package Publication
 */

get_header(); ?>

	<div id="primary" class="content-area">
		<main id="main" class="site-main" role="main">

		<?php if ( have_posts() ) : ?>

			<?php /* Start the Loop */ ?>
			<?php while ( have_posts() ) : the_post(); ?>

				<?php
					if ( ! is_paged() && 0 === $wp_query->current_post && has_post_thumbnail() ) {

						get_template_part( 'template-parts/content', 'hero' );

					} else {

						/*
						 * Include the Post-Format-specific template for the content.
						 * If you want to override this in a child theme, then include a file
						 * called content-___.php (where ___ is the Post Format name) and that will be used instead.
						 */
						get_template_part( 'template-parts/content', get_post_format() );

					}
				?>

			<?php endwhile; ?>

			<?php
				the_posts_navigation( array(
					'prev_text' => '<span class="meta-nav">' . esc_html__( 'Older posts', 'publication' ) . '</span>',
					'next_text' => '<span class="meta-nav">' . esc_html__( 'Newer posts', 'publication' ) . '</span>',
				) );
			?>

		<?php else : ?>

			<?php get_template_part( 'template-parts/content', 'none' ); ?>

		<?php endif; ?>

		</main><!-- #main -->
	</div><!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>