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Let us create a learning exercise with dual task, using the CA8 program. It must be an extremely tense position, where White has a sole solution to the task when it is White's turn to move, and if it is Black's turn to move, then Black can win in only one way! Note that you can find over 200 positions of this kind either in the CT-ART 3.0 program, or in grandmaster Maxim Blokh's books: 1200 combinations, The art of combination, Combinative motifs, 600 combinations.
Let us explore using the combinative motif of opposition in realizing a combination/tactical method of discovered attack as a theme. First, we must compose and arrange on the board a preliminary project of our position, employing some formal conceptions and templates.
The white b1-rook is in opposition with the black b8-rook. The Bxg7+ move allows White to realize a discovered attack. The black d7-queen is in opposition with the white d2-queen. Black can conduct the similar discovered attack by the Bxg2+ move after having enticed the white king to h1 by means of the rook sacrifice 1. Rh1+!. Let us start now the multivariation analysis mode for both sides.
As we can see, for White, apart from the thematic 1. Bxg7+! Kxg7 2. Qg5+ Kh7 [2Kf8 3. Rxb8+] 3. Qh4+! (a herring-bone maneuver!) 3... Kg7 4 Qg3+! Kh7 5. Rxb8 Rxb8 6. Qxb8 +-, the program suggests also 1. Qg5! f6 2. Bxf6! Rxb1 3. Rxb1 +.
While for Black, after 1...Rh1+! 2. Kxh1, instead of the thematic continuation 2... Bxg2+, the program suggests the quicker and more efficient 2...Qh3+! 3. Kg1 Qxg2#.
Let us select the item Define position in the local menu of the board and modify the position. In order to refute the threat of Qh3xg2#, let us add the white f1-bishop. We have also to add the black bishop for maintaining the material balance. It is very difficult to place this piece on the board without disrupting the set-ups of both sides. Let us try the c5-square. In this case however, when both black bishops target the white kings position on the adjacent diagonals, a horrible non-thematic threat is available for Black: 1... Rxb2 !! [1Qc7 ? 2. Be5! ] 2. Rxb2 Qc7!+. To remove it, add the black c7-pawn. Now failing is 1...Rxb2?? 2.Rxb2 Qd6? due to 3. Rb8+. But then White loses an opportunity of capturing the rook by the diagonal attack along g3-b8 after 1. Bxg7+! Kxg7 2. Qg5+ Kh7 3. Qh4+ Kg7 4. Qg3+. It doesn't matter! The newly emerging f1-bishop comes to Whites aid. Instead of 3. Qh4+, White can play now 3. Bd3+! f5 4. Bxf5+ +.
After having added the necessary modifications to the diagram (the white f1-bishsop, the black c5-bishop and the black c7-pawn added), press OK and continue to work in the multivariation analysis mode for both sides.
The program indicates a marginal winning opportunity for White (without the sacrifices), the one of 1.Qc3!, creating a double attack on g7 and c5. Thus, the black c5-bishop becomes an Achilles heel of our design! What do we do with this piece?! It cannot simply be placed on some other square, it is impossible to protect it with a pawn, since neither b-, nor d-file can be interposed.
Well, what about protecting it with the white f1-bishop by placing the latter on c4!? Then, however, Blacks threat is resumed, the one of: 1... Rh1+! 2. Kxh1 Qh3+!! 3. Kg1 Qxg2#. In order to remove it, let us place the black a5-pawn to g4.
After having made the necessary modifications (the white f1-bishop placed on c4, the black a5-pawn placed on g4), continue the multivariation analysis for both sides.
It all seems to be quite right now. White has a single thematic way to win:
1.Bxg7+! Kxg7 2. Qg5+ Kh7 [2Kf8 3. Rxb8+] 3.Bd3+ f5 4. Bxf5 +.
Black also has a single thematic way to win: 1...Rh1+!! 2. Kxh1 Bxg2+! 3.Kxg2 Qxd2 +.
However, Black may choose to continue: 1...Ra8 ?! /+. But it is extremely difficult to balance the sharpest double position taking into account all the lateral continuations for White and for Black. The readers may continue this exciting process on their own using the technique described above. I wish you the best of luck in your endeavors!