How do you checkmate with a lone cannon, and when is a cannon alone not enough?
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
You cannot. A cannon checks only by jumping exactly one screen, and against a bare general there is none: your own general can never serve, because on a file the two generals would face each other and the two palaces share no rank. So a lone cannon cannot even give check, and it draws all 4,914 legal positions. It needs a second piece, such as an advisor or a soldier, to mate.
Why the screen requirement is the whole problem
Without a screen, a cannon cannot check the general at all, since it cannot capture anything without jumping one piece first. With only the two generals and the cannon on the board, the only candidate is your own general, and it can never stand between the cannon and the enemy general: on a file the generals would face each other with nothing between them, which is illegal, and on a rank they never meet, because the palaces are on different ranks.
What it takes instead
One more piece. Cannon and advisor wins, with the advisor as the screen; cannon and soldier wins 86.8% of positions; horse and cannon wins every one. The counts are on the proven endgame verdicts. In practice, cannon endgames are almost always paired with at least one other piece for exactly this reason.
Related questions
Is cannon and advisor a more reliable combination?
Yes, it wins; see mating with cannon and advisor for that technique.
Can a lone cannon ever draw against a bare general?
It always draws. All 4,914 legal positions are drawn, because a cannon with nothing to jump cannot give check, let alone mate.
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