listing categories and posts of current category: is_single problem

Hi all,

so i have the following code:

<?php
    // get all the categories from the database
    $cats = get_categories(); 

        // loop through the categries
        foreach ($cats as $cat) {
            // setup the cateogory ID
            $cat_id= $cat->term_id;
            // Make a header for the cateogry
            echo '<h2><a href="./?cat='.$cat->term_id.'">'.$cat->name.'</h2>';
            // create a custom wordpress query
query_posts("cat=$cat_id"); ?>
   <?php if (in_category($cat_id)) { ?>
<?php  if (have_posts()) : while (have_posts()) : the_post();     ?>
                <?php // create our link now that the post is setup ?>
                <a href="<?php the_permalink();?>"><?php the_title(); ?></a><br>
          <?php endwhile; ?> <?php endif; // done our wordpress loop. Will start again for each category ?>
    <?php } else { ?>
<?php } ?>
  <?php } // done the foreach statement ?>

this code makes my category post show when i’m on that current category page. I wanted to add the following thing in the have posts loop (it should make Yes appear under EACH the post title on single post 84, and no everywhere else… :

<?php if (is_single('84')) {  ?>
Yes
<?php } else { ?>
no
<?php } ?>

But: is_single seems not to be working inside the loop. when i put it outside the loop it works in combination with a wp_reset_query prior to the code, but i really need it inside the loop.

I dont know if this is proper code, but i’m learning as im doing it actually, so be easy on me ??

thanks!

edit:
a screenshot perhaps!
SCREENSHOT