This particular puzzle had a clue of the type: "Of A and B, one is C, and the other is D."
The technique used for this type of clue also works for its onesided version of the type: "A is either C or D."
Find out what elements of D that C can never be and what elements of C that D can never be, and then apply those exclusions to A.
You're finding out what the right side of the equation can never be and reflecting that on the left side.
Note that if the two elements on the right side are in the same category, you won't get any bonus Xs.
The clues of type: "Of A and B, one is C and the other is D", are a great place to go hunting for Xs.
Find out what the left side can never be and reflect that on the two elements of the right side, and then find out what the right side can never be and reflect that on the two elements of the left side.
"Find out what the left side can never be" means find the elements of B that A can never be, and find the elements of A that B can never be.
Graphically, you're just checking the row and column containing the A B intersection for bonus Xs.
If you process these types of clues a little later in the sequence, you will have more potential for those bonus Xs.
