How do you defend against a double cannon (重炮) check?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
A double cannon check is given by the rear cannon, using the front cannon as its screen. You can escape by moving the general off the line, capturing the rear cannon, taking an undefended front cannon with the general, or putting a piece between the two cannons. What does not work is putting a piece between the front cannon and your general: that gives the front cannon a screen, and it checks instead.
Count the pieces on the line
Every cannon check depends on exactly one piece standing between the cannon and the general. In 重炮, the line reads: rear cannon, front cannon, your general. The rear cannon has one screen, so it checks. The front cannon has no screen, so it does not.
Now test each block. A piece placed between the two cannons gives the rear cannon two screens: no check from either cannon. A piece placed between the front cannon and the general gives the rear cannon two screens but the front cannon one: the front cannon now checks. That is why the pattern feels unblockable, and why the classic mate has the front cannon sitting right next to the general with no gap at all.
The other escapes
- Step off the line. Usually the reason it is mate is that your own advisors fill those points.
- Capture the rear cannon. Removes the checking piece.
- Capture the front cannon with the general. Possible only when it stands right next to the general and nothing attacks that point once the general arrives. Capturing it with another piece does not help, because that piece becomes the new screen.
Preventing it
Keep a piece that can reach the gap between the cannons, keep your general's sideways points available, and treat an enemy cannon arriving on your general's line as a warning, not a curiosity. The existing explainer on what 重炮 is lists the conditions the attacker needs.
Related questions
Does this work along ranks too?
Yes. Cannons capture along ranks as well as files, so a double cannon line can run sideways across the palace.
Is 重炮 always mate?
No. It is mate only when every escape above is closed at once.
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