< or <= is a choice. it was made in favour of <.

== can be derived from <= but not <, but that's no reason to choose <= over <.

Closing.

fixed

Imagine you have to calculate each angle as cos from scalar product of vetors corresponding the sides of the angle...

The sturcture of these two arrays is actually the same. ']' is equivalent of a symbol or any non-list structure, so basically both original and other are equiv to [1, 1, 1]

Python tests are bad. Simple invalid solution can pass through
https://www.codewars.com/kata/reviews/554662240240a7b6f800019c/groups/5fe56d3e1c498800017567f9

I believe "≺" should be reflexive, since connexity must hold: ∀ a,b ∈ Set (a≺b or b≺a). It means sharkovsky(a, a) should return True.
If not, an addition to the description should be done anyways.

The description says that the first letter of each word must be capitalized, but it doesn't say you need to change all other letters to lower case.
So this is kinda unexpected in Python at least. People in the comments say it may depend on the language. Strange. A good kata should have a clear description so the description should be clarified.