Can you help add the PERFORMANCE tag?

Already added by somebody.

You're right, the solution did not cover those cases.
I like your modifications.

Fixed

Merged

Thanks for the explanation. I mistakenly thought that would result in undefined behavior.

.

Except shadowing the built-in function input, it seems okay.

Is it possible to have more than one K?

Python sample test

File "/workspace/default/tests.py", line 8
    test.assert_equals(next_higher(1), 2)
IndentationError: unexpected indent

I think the author should either increase maximum recursion depth or find an alternative way to implement make_sequence, for example, use a while loop.

All should be fixed in the new commit.