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<?
// From https://wp-snippet.com/snippets/remove-author-prefix-from-slug/
add_filter('author_rewrite_rules', 'no_author_base_rewrite_rules');
function no_author_base_rewrite_rules($author_rewrite) { 
    global $wpdb;
    $author_rewrite = array();
    $authors = $wpdb->get_results("SELECT user_nicename AS nicename from $wpdb->users");    
    foreach($authors as $author) {
        $author_rewrite["({$author->nicename})/page/?([0-9]+)/?$"] = 'index.php?author_name=$matches[1]&paged=$matches[2]';
        $author_rewrite["({$author->nicename})/?$"] = 'index.php?author_name=$matches[1]';
    }   
    return $author_rewrite;
}
 
// The second part //
add_filter('author_link', 'no_author_base', 1000, 2);
function no_author_base($link, $author_id) {
    $link_base = trailingslashit(get_option('home'));
    $link = preg_replace("|^{$link_base}author/|", '', $link);
    return $link_base . $link;
}