This is the classic result of formal language theory, but there is too much slack between context free and context sensitive, which is PSPACE (larger than NP!).

By Noam Chomsky.

A good summary table that opens up each category much more can be seen e.g. at the bottom of en.wikipedia.org/wiki/Automata_theory under the summary thingy at the bottom entitled "Automata theory: formal languages and formal grammars".

There is a Turing machine that halts for every member of the language with the answer yes, but does not necessarily halt for non-members.

Non-examples: cs.stackexchange.com/questions/52503/non-recursively-enumerable-languages

2021-01-28: used this show for the first time after wearing dhb Dorica MTB Shoe (2020-12) exclusively for a while. It felt much much more comfortable, the Dorica is too narrow. Also this one is much more recessed, and walking with it is much easier. Also, I notice that the intentional asymmetry I had put on cleats is not necessary anymore now that my saddle height is not way too high

At 5C feet are too cold. Compatible overshoes are basically impossible to find: bicycles.stackexchange.com/questions/73589/what-kind-of-overshoes-can-i-use-with-a-large-touring-spd-cycling-shoe-such-as-t

It is not possible to do long walks with this, unlike some websites suggests, especially on hard surfaces like rock, that would be very dangerous because the cleat area will slip. But it is good for shorter walks on grass/mud, and that does open up some good short walk exploration possibilities compared to a road shoe.

Color "Black/Red 20" (but it's actually orange), size 46 www.wiggle.co.uk/giro-rumble-vr-off-road-shoe (archive). Manual says to use Loctite 243 medium strength, first 2.4 Nm bolt torque to test it out and find good position, and then final bolt torque 5-6 Nm unless cleat says less. Starting with Shimano SM-SH56 cleats (archive), which also says provisional torque 2.5 Nm, tightening torque 5-6 Nm.

Subset of recursively enumerable language as explained at: difference between recursive language and recursively enumerable language.

Set of all decision problems solvable by a Turing machine, i.e. that decide if a string belongs to a recursive language.

Organelle that is only present in prokaryotes.

Is a decision problem of determining if something belongs to a non-recursive language.

Or in other words: there is no Turing machine that always halts for every input with the yes/no output.

Every undecidable problem must obviously have an infinite number of "possibilities of stuff you can try": if there is only a finite number, then you can brute-force it.

Some undecidable problems are of recursively enumerable language, e.g. the halting problem.

Lists of undecidable problems.

Coolest ones besides the obvious boring halting problem:

A:

The prototypical example is the Busy beaver function, which is the easiest example to reach from the halting problem.

There are only boring examples of taking an uncomputable language and converting it into a number?

The list: complexityzoo.uwaterloo.ca/Complexity_Zoo

The canonical undecidable problem.