Transparency in a matte layer

[cedric5DB9]

I've gotten a lot further on this on my own than expected, and I'm one step away, but it's sadly failing me. This is an animation (self fueled learning project) of two precomposed matte layers crossing over each other and setting into corner postions in the screen. One moves from right to left, the other from left to right. My question is how to make the intersection of them transparent so that it just shows the blue background. So far, no combination of matting and inverting mattes have done the job. Visibility, alpha, luma options don't seem to get me what I want. My best lead thus far is to change the actual precomp (duh) to being transparent, but that makes the the images themselves go away. Is there a null object solution (???) or is there something I'm not seeing?

Worth noting, they are both the same precomp, but I rotated one by 180 degrees, if that's important.

Thanks for your help!

[Mylenium]

The answer is more pre-composing or possibly something like the Stencil/ Silhouette Alpha blending mode. Also the Set Matte effect still exists (as do other Channel effects) to introduce the cutout after the matte operations. A million ways to do it , you just need to wrap your head around it and not expect that this can be solved in a single comp or for that matter no layer duplicates. You have to establish a consistent A-B logic and the subtract C in the next step.

Mylenium