Are all these puzzles uniquely solvable?
Only when the stated constraints justify it. Our worked grid, bounded remainder riddle, cabinet code and drawer challenge include uniqueness arguments. An unrestricted pattern sequence may admit multiple rules. A valid counterexample should prompt scrutiny of the question, not automatic dismissal of the solver.
Does using a hint invalidate my solve?
No. Record which hint you used if comparing attempts, then try to reproduce the reasoning later without it. A first hint usually suggests a representation; later hints narrow the deductions. Solutions remain separate so you can stop before the final answer.
How is difficulty assessed?
We discuss the required technique and reasoning steps rather than claiming an IQ threshold. Difficulty depends on experience and representation. Some worked examples are deliberately compact so their proof structure can be inspected. “Extreme” describes the wider pursuit, not a scientifically calibrated rating for every exercise.
What does impossible mean here?
It means no solution satisfies the published contract when an impossibility proof is supplied. It is not shorthand for a low success rate. The first matchstick contract is impossible because the required arithmetic target violates a preserved segment count; its companion contract is solvable.
Can I solve without JavaScript?
Yes. Written challenges, native hint accordions and solution reveals remain available. Automatic checking and contact draft generation require JavaScript. You can still email a written question directly using the address in the footer.
Are competition results public?
No. The home-page ladder checks three entries locally. There is no account, leaderboard, prize or certified ranking. Counts reset when the page reloads. For an informal comparison with friends, agree in advance on hints, timing and what constitutes a complete proof.
Are hints and answers hidden from assistive technology?
They use native details and summary controls, which expose their expanded state. Essential puzzle information is available as text. Photographs are illustrative, and color alone never carries a required clue. If a control is difficult to use, describe the browser and interaction in a diagnostic message.
What should I send when reporting another answer?
Send the page, exact rule interpretation, candidate answer and a step-by-step verification. Include both the source and destination of any moved matchstick. The contact tool prepares a draft but does not send it. Do not include passwords, sensitive personal information or copyrighted puzzle packs.
Can I reuse the explanations?
Link to the pages freely. Seek permission before substantial republication, subject to applicable copyright exceptions. Third-party material may have separate rights. Historical puzzle mechanisms are not the same thing as permission to copy a publisher’s wording, diagrams or photographs. See our terms for further details.