How does a defender with a full advisor-and-elephant setup actually hold a draw against a lone horse or a lone cannon?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
By simply not moving anything unnecessarily. Neither a lone horse nor a lone cannon can force checkmate against a bare general, and adding a complete advisor-and-elephant defence around that general makes the position even further out of reach: the defenders have more than enough pieces to cover every point the lone attacker could threaten, and they are under no pressure to create a weakness by moving.
Why the attacker cannot make progress alone
A horse can be blocked at its leg by the defender's own pieces, and a cannon needs a screen it does not have inside an empty palace. Against a full set of advisors and elephants, the lone attacking piece simply cannot threaten enough points at once to force a defender to abandon a key square, so no combination of threats ever actually lands.
The one thing the defender must avoid
The only real danger is self-inflicted: moving a defender to an exposed square for no reason, or trading away a defensive piece that did not need to go. As long as the defence stays intact and simply mirrors the attacker's approach, the position is a completely safe, standard draw.
Related questions
Does this change if the attacker also has a soldier?
Yes, a horse or cannon paired with a soldier is enough to force mate; it is only the bare piece alone that falls short.
Is this the same reasoning as the insufficient-material rule?
Yes, this is the practical, move-by-move version of why a lone horse or lone cannon is listed as insufficient material to force a win.
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