Artificial Intelligence / Unit 4 AI 0190 worked example, 60 to 90 seconds
Propagation at the Festival
The idea
Running propagation on the festival deletes twelve conceivable values down to eight and demolishes the doomed subtree before any search begins.
In practice
Track the four domains. The fireworks rule collapses Cinder to 3 alone. The van rule strikes Brook's 1, leaving 2 and 3. The opener rule works both directions: Anvil = 1 dies because no Dune slot is earlier than 1, and Dune = 3 dies because no Anvil slot is later — Anvil keeps 2 and 3, Dune keeps 1 and 2. Count the survivors: two, two, one, two — the 81 conceivable schedules have quietly become 2 × 2 × 1 × 2, eight. And notice what vanished: the entire Anvil = 1 drawer, which backtracking disproved by exhaustive failure, was deleted here by one line of reasoning, before a single assignment was tried.
Where people slip
Every deletion was pure logic — no schedule tried, no guess made, nothing legal lost.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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