Do we really want to delete undecidable answers, even if they were declared non-competing?

The problem emerged with this answer (deleted, and so invisible for users with less than 10k reputation)

The most relevant win criteria of the puzzle is the algorithmic complexity of the solution.

An answer using Mathematica was posted, making the algorithmic complexity of the solution depending heavily on the internal algorithms used by this software. These are not enough well known, and practically unknowable, because Mathematica is closed-source software.

However, the solution seemed a quite interesting one for me, and maybe also for others (it got multiple upvotes).

Accepting the situation, the poster declared the solution as non-competing.

Despite that, it was deleted by community votes.

I think, also non-competing or undecidable answers improve the site. However, it would be probably not useful to have a large mass of non-competing, unanswerable answers. Furthermore, the primary goal of the site may be to collect mainly competing answers to the puzzles.

Yes

Non-competing doesn't allow an answer to do what it wants, and not meet the questions specifications. If a question has a specific scoring system, answers whose scores can't be calculated shouldn't be marked non-competing, they should be removed from the question.

In short, if I posted an answer to the Hello, World! question that didn't display Hello, World!, is it a valid answer? No. Can it be marked non-competing? No. To quote Dennis,

Marking an answer as non-competing does not exempt it from being invalid.

The Mathematica answer, while being interesting, did not meet the answer specification, and, per our rules it should have been deleted. This also applies to any other answers which, while accomplishing the task at hand, can't be scored.

• What if it actually prints hello world, and it may fulfill the criteria, but nobody can check it for sure? Sep 24 '17 at 16:14
• @peterh what criteria? Sep 24 '17 at 16:14
• The win criteria of the question. In this specific case, the algorithmic complexity of the solution couldn't be determined, although it solved the problem. Sep 24 '17 at 16:15
• @peterh if it can't provably complete the task, and can't have an objective, determinable score, it isn't a valid answer Sep 24 '17 at 16:19
• A better analogy would be a 'Hello, World!' program where for some reason you can't possibly determine the byte count (think of a tokenized language like TI-BASIC, but then one that does not reveal how many bytes each token is). It performs the task, but you cannot determine the score. Sep 25 '17 at 13:35
• Of course, if the question explicitly allows non-competing answers, they should be allowed per this meta consensus. Oct 4 '17 at 2:31