Thanks to ShriekingViolet for pointing out this technique and Zenobia43 for spelling it out in detail.
Puzzle Baron's YouTube video on solving techniques has an example of overlapping binary relational sets. THIS LINK
will take you to the exact point in the video where it is pointed out (be sure to hit pause so you can read the text).
The video points out that there is a value relationship between two values in the same category, both of which have two potential values, and that these values overlap. In the video this relationship can be written as "$5.35 is either Diet Coke or Orange Soda". This eliminates all other values of sodas for "$5.35".
What ShriekingViolet pointed out IN THIS THREAD
, is a technique for making this same overlapping binary relationship between values in two DIFFERENT categories.
I've spelled it out in this graphic:
It essentially boils down to this:
When there are only two potential values for each element in a fixed relational clue, and one value, A, exists for each element, B and C, you can write the relationship as “A is either B or C”.
It's a clue that is as valid and useful as the clues you are given, but it's hidden in the puzzle.