Puzzle-metapuzzle pairs

When at school, I beleved that a good puzzle should have a solution. In my first year at college I encountered the idea of a "solution set". This was mind-expanding. A puzzle has a set of solutions: often the set has one member, but it may have none, or many.

When I was at college, I came across puzzles like this:
     If dimF v = n prove that dimF (Hom(V,V)) = n2.
I realised that the setter will have been thinking "the pupil will know what all this stuff means. The challenge is to find a proof." In reality, the pupil might not know what, say, dimF means. The challenge is then to come up with a plausible meaning for dimF such that the proof is possible but not trivial.

I regard such puzzles as metapuzzle/puzzle pairs. The metapuzzle is to come up with a plausible interpretation of the puzzle statement; the puzzle is to solve that interpretation. If the puzzle is too easy or too hard, maybe you've got the metapuzzle wrong.

I once regarded such metapuzzle/puzzle pairs as a defective puzzles, which had accidentally acquired a metapuzzle wrapping. Now, I regard any puzzle statement as a metapuzzle/puzzle pair. Sometimes the metapuzzle is trivial, but I don't know that until I've solved the puzzle, or at least convinced myself that it may well have an interesting solution. This viewpoint doesn't just apply to abstract algebra puzzles like the one above, but also to some old chestnuts like "what colour is the bear", "manhole covers", and "Monty Hall" in the list below.

Some examples

Accidental metapuzzles resulting from careless wording of the problem statement

Four colliding ships

The Monty Hall puzzle

Six points on a disk

Ants and triangle

Simultaneous equations

Doppler effect question

Square question

Deliberate metapuzzles with problem statements that are intended to misdirect or to be hard to parse

Two points on the equator

A sliding block puzzle

Numbers in a car park

Square square pyramidal number

"Found" metapuzzles where the lack of a clear puzzle statement is not due to the puzzle's creator

Wooden puzzle

Plastic puzzle

Bolleke puzzle on beermat

Undecided which category is most appropriate

What colour is the bear?

Manhole covers

Other

Tornado question

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