How do two cannons attack on different files in xiangqi?
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
Instead of stacking on a single file for 重炮, two cannons can work from two different files at once, each with its own screen, each threatening a separate point near the palace. The defender then faces two independent problems rather than one, and answering one line often does nothing for the other.
Why splitting can be stronger than stacking
A stacked pair, 馬後炮's cousin pattern, needs the front piece defended and the general boxed in. Two cannons on separate files need neither: each is a separate threat in its own right, so the defence has to solve two problems with pieces that may only be able to help with one.
The coordination it actually needs
Both files need their own screen already in place, or arriving on schedule, and both threats need to land close enough together in time that the defender cannot simply deal with the first before the second arrives. Timing, not just positioning, is what makes the split pair work.
Related questions
Is this pattern as strong as 重炮?
Different rather than stronger or weaker: 重炮 is a forced mate once set up, while a split pair creates pressure that still needs converting.
Can a single defender handle both files?
Sometimes, if the defender's remaining pieces cover both lines. That is exactly the calculation worth doing before committing to the plan.
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