{"id":"island-perimeter-subtract-two","text":"Each shared edge between two land cells removes exactly 2 from the perimeter total; checking only up and left neighbors (not all four) guarantees each adjacency is counted exactly once because the scan is top-to-bottom, left-to-right.","truth_value":"IN","source":"entries/2026/06/06/island-perimeter-solution.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{},"created_at":"","updated_at":"","reviewed_at":"","verified_at":"","retracted_at":"","explanation":{"steps":[{"node":"island-perimeter-subtract-two","truth_value":"IN","reason":"premise"}]}}