The programming languages list contains a note "Added Haskell and F#", but I can't find it in the drop-down list of languages. Is it or was it ever available for submitting solutions?

In the submission http://mirror.codeforces.com/contest/577/submission/12949782 I first printf "YES" and then I printf some numbers. In the output, the numbers came out first and then the "YES". Documentation for std::ios_base::sync_with_stdio generally seems to indicate that bad effects from disabling it should only occur if you use both C- and C++-style I/O. Here I only used C-style output throughout, yet the print statements were mixed. Is this really an allowed behavior for the library?

Is there a way to view the messages generated by compiler errors in a Codeforces submission? Twice today I have been bedeviled by mysterious errors which do not occur in my personal copy of GCC. At least I was able to view the uploaded source code and verify that it was what I thought I was submitting.

Is there any way to hide the tags when solving past problems? I want to think about them for myself, so it is irksome when the tags are telling me I should use (greedy), (dfs) and so on.

Is there a stupid trick to calculate n-choose-k for a range of n with k always the same, which is faster than forming the full Pascal's triangle? With some fixed k, I need to calculate all n-choose-k modulo 10^9+7 for n up to 100,000 but there's no way I can calculate all the coefficients within 3 seconds.