Puzzles — Revision Notes

⚡ 30-Second Revision

Translate, place, propagate, branch, check. Before ≠ immediately before. Could: one valid witness. Must: every valid arrangement. Keep temporary assumptions separate from confirmed facts.

2-Minute Revision

Use rows for order, grids for multiple attributes and blocks for immediate adjacency. In the four-day example, D–B can start on three days; the first two violate C-not-Thursday, leaving A, C, D, B. A completed arrangement must satisfy every clue. Facing south reverses page-left and personal-left on a conventional map.

5-Minute Revision

Solve the four-day puzzle without looking at its answer and write the reason each rejected block placement fails. Next compare A–B–C–D with A–C–B–D: identify a must-be-true statement, a merely possible statement and an impossible statement. Explain why a valid counterexample defeats a necessity claim.

Vyyuha Quick Recall

One witness for could; every case for must.