Learn Finnish: Yhtiön ohjeistus vaatii, ettei kukaan riko lakia. - The company's guidelines require that no one breaks the law.

Ettei is a fusion of the conjunction että (that) and the negative verb ei (not). The negative verb always matches the subject of its own clause. Because the subject here is kukaan (no one), which takes the 3rd-person singular, the negative verb is ei. They combine into ettei (that not).

Why do we use kukaan instead of joku here?

Kukaan is the negative equivalent of joku (someone/anyone). Whenever a clause is negative, as it is here due to ettei, you must use kukaan to mean "no one" or "anyone". Using joku in a negative clause sounds unnatural in Finnish.

Why is the verb rikkoa (to break) written as riko?

Since the clause is negative, the main verb must be in the present connegative form (the form used after a negative verb). You find this by taking the "minä" form (rikon) and dropping the -n. Notice that it undergoes consonant gradation, weakening the double kk to a single k.

Why is laki (law) in the partitive case (lakia)?