Learn Turkish: Hiçbir kanıtı kaybetmeyiz. - We do not lose any evidence.

It disappears! This is the special rule for the 1st person ("I" and "we") in the aorist negative. While the positive form has an -r- (kaybederiz - we lose), the negative drops it. We just use the verb root kaybet, the negative marker -me, and the "we" ending -yiz to make kaybetmeyiz.

Where does the verb kaybetmek come from?

It is a compound verb made from kayıp (lost) and the helper verb etmek (to do/make). When they join, two things happen: the second vowel in kayıp drops out, and the p softens to a b. That gives us kaybetmek (to lose).

Why is it kanıtı and not kanıdı? Doesn't t usually change to d before a vowel?

Yes, normally a t at the end of a word changes to a d when you add a vowel suffix like the accusative -ı. However, several Turkish words ending in the suffix -ıt (like kanıt for evidence, or taşıt for vehicle) are exceptions to this rule and keep their hard t.

Is it normal to use hiçbir with a negative verb?