I should have been more specific - what I meant is that the ads that instagram chooses to show you can be thought of as points in ad-space. So when you click on

I should have been more specific - what I meant is that the ads that instagram chooses to show you can be thought of as points in ad-space. So when you click on ads and instagram chooses to show you different ads as a result, you have traveled around in this space. I say the space is metric because it is meaningful to say that two ads are more or less similar. I assume the "click all ads" mapping is contractive because if you take two different people with different histories of clicking ads and therefore different flavors of ads shown to them, and they both just start clicking on all ads regardless of content, the ads they both see after doing this should be more similar, or closer in ad-space. So iterating this should just get to a point where they see the same ads (or at least ads that are progressively similar)