Is there a way to filter the next/previous navigation so that when you read a full post, only posts in that category show up in the navigation?

What would want to do if the post was in multiple categories?

For this particular site that's not an issue. Can it be done?

it looks like the theme is using the standard WordPress nav code (wp-inlcudes/link-template.php)
so you might be able to hack at that and change how it is getting the next and previous links

Hello JuggleDad
What a job you've got processing all these queries!
I think this thread is something like the problem I'm having with Ata navigation and multiple post categories.

When a post has multiple categories, the bfa_navigation code chooses the 'default' category (with the lowest ID). Choosing any other category from the site menubar (other than the default) means that the navigation does not show the other posts in that category.

I'm using the latest version of everything, and have tried "sCategory Permalink" to change the default category, but to no avail. Is there any modification I can make to Atahualpa ?

Kind regards.

Are you trying to say that if you browse a category, the next/previous could take you into a new category?