我是php新手，我正试图弄清楚为什么会发生以下错误：

Notice: Undefined variable: post in functions.php on line 59

<?php

// related pages
function wpb_related_pages() {
    $orig_post = $post;
    global $post;
    $tags = wp_get_post_tags($post->ID);

    if ($tags) {
        $tag_ids = array();

        foreach($tags as $individual_tag)

            $tag_ids[] = $individual_tag->term_id;

            $args=array(
            \'post_type\' => \'page\',
            \'tag__in\' => $tag_ids,
            \'post__not_in\' => array($post->ID),
            \'posts_per_page\'=>4
            );

        $my_query = new WP_Query( $args );

        if( $my_query->have_posts() ) {
            echo \'<div id="relatedpages"><h3>Related Terms</h3><ul>\';

            while( $my_query->have_posts() ) {
                $my_query->the_post(); ?>
                <li>
                    <div class="relatedthumb">
                        <a href="<? the_permalink()?>" rel="bookmark"     title="<?php the_title(); ?>"><?php the_post_thumbnail(\'thumb\'); ?></a>
                    </div>
                    <div class="relatedcontent">
                        <h4>
                            <a href="<? the_permalink()?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a></h4>
                            <p>
                                <?php $content = get_the_content(); echo mb_strimwidth($content, 0, 90, \'...\');?>
                                <a href="<?php the_permalink() ?>"> Read More</a>
                            </p>
                    </div>
                </li>
            <?
        }
        echo \'</ul></div>\';
        } else {
            echo "No Related Pages Found:";
        }
    }

    $post = $orig_post;
    wp_reset_query();
}
?>