There's a popular type of maths puzzle where you get a list of digits (or numbers in general) and need to insert arithmetic operators in order to reach some target number. Every single time we get a challenge around this topic, I think "this looks so familiar, we must've done this before", but then I always fail to find a dupe target, because these challenges are near impossible to search for. The keywords that come to mind are things like "expression", "equation", "operator", "operation", "insert", "arithmetic", "Countdown", "Lettres et chiffres", etc. But these are all so horribly general that they turn up way more false positives than the actual challenges you're looking for. And then there's the problem that everyone seems to describe the problem differently, so you're probably overlooking some challenges all together.

But that's what tags are for. They group related challenges. If we introduced a tag for this, that would make it a lot easier for the experienced users to find existing challenges around this topic in order to look for duplicates. Of course it would also help people find similar (non-dupe) challenges similar to the one they've just solved, if they liked it.

So there's two things to this: a) coming up with a good tag name, b) finding all the relevant challenges so we can tag them. I've done some hunting just now, mostly via linked challenges and a few lucky keywords and here's what I dug up:

There are also a few challenges where I'm not 100% sure whether they should be covered by the tag or not, but they're definitely closely related:

And then there's (at least) two challenges where you don't generate an expression given a list of digits, but instead you need to write a program which contains the digits in the given order and prints some result:

These are definitely a bit different, but I feel like they're still in the same spirit.

As Mitch Schwartz pointed out in chat, certain metagolf challenges are also closely related. For example:

So, please let me know what you think about the utility of such a tag, what such a tag should cover, whether I've overlooked any challenges and of course any suggestions for a tag name.

  • \$\begingroup\$ What about that one? \$\endgroup\$
    – Fatalize
    Commented Jun 14, 2016 at 12:50
  • \$\begingroup\$ @Fatalize Wow, I've never seen that one. What a lovely challenge. :) I'm not entirely convinced it should be covered by this tag though because it actually seems quite different. (But I'm happy to be convinced otherwise by an answer.) \$\endgroup\$ Commented Jun 14, 2016 at 12:58
  • \$\begingroup\$ I'm not sure either. The tag would apply to most answers but not to the challenge itself I think. \$\endgroup\$
    – Fatalize
    Commented Jun 14, 2016 at 13:00
  • \$\begingroup\$ I always search for "Countdown numbers game", and am regularly surprised not to get any hits. I'm not sure that we need more than two open versions of this genre: one for the basic operations (+-/*) and one (probably Four Fours) which allows a wider set of operations. \$\endgroup\$ Commented Jun 14, 2016 at 13:32
  • \$\begingroup\$ Here's another example: codegolf.stackexchange.com/questions/79743/… \$\endgroup\$
    – DJMcMayhem
    Commented Jun 14, 2016 at 21:01
  • \$\begingroup\$ I feel like generation could cover this \$\endgroup\$
    – Downgoat
    Commented Jun 16, 2016 at 19:16
  • 1
    \$\begingroup\$ @Upgoat I kinda want that tag to die a horrible death because its name is so ridiculously general and non-descriptive, it seems completely useless to me. \$\endgroup\$ Commented Jun 16, 2016 at 21:51
  • \$\begingroup\$ @MartinEnder that is true you could probably tag 99% of questions here as "output generation" \$\endgroup\$
    – Downgoat
    Commented Jun 16, 2016 at 22:00
  • \$\begingroup\$ Maybe just math-operators. \$\endgroup\$ Commented Jun 17, 2016 at 17:57

3 Answers 3


I think having a tag for this is a good idea. The other solutions are great, but I'm going to throw out another one:


This seems to be the most popular solution, so I went ahead and created this tag. I'm going to slowly edit it into the questions that Martin has linked (to avoid flooding the front-page).

The tag wiki is here. Feel free to edit if you think you can improve clarity on it.

  • 3
    \$\begingroup\$ I definitely prefer something with "expression" to something with "arithmetic" or "number", just because it's a bit more general. \$\endgroup\$ Commented Jun 14, 2016 at 21:01
  • \$\begingroup\$ @MartinEnder On the other hand, "expression" does also have a programmatic meaning though, as in "building an expression to be evalled". Or was that your intention? \$\endgroup\$
    – Sp3000
    Commented Jun 16, 2016 at 8:23
  • \$\begingroup\$ @Sp3000 I'm actually a bit on the fence about that. On one hand where do you draw the line between arithmetic and program code, on the other hand, do we want all metagolf challenges to be tagged with this? (Also, due to the examples from Mitch I noticed that we currently can't really tag metagolf-related challenges where metagolf isn't used as the winning criterion...) \$\endgroup\$ Commented Jun 16, 2016 at 9:56

On Puzzling.SE, we use the tag for this purpose.


I think would be a pretty good choice.

On a more serious note, would be good.


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