Looking for a "н"

Trying to find Russian language something less difficult I study also in Alphadictionary russgrammar. I try to find the link between (за)ня-ть и (за)йм-у. It is said: "In non-syllabic roots 'н' and 'м' are replaced by 'a' before a consonant ending". So, if I suppose that the stem is йм-, it will become in the infinitive, for example, йa- -> я , that is, (за)[н]я-ть. But this "н" was in the stem and has disappered ? I don't find in these lessons, very complete on other hand, no explanation to this case. I find also other verbs similar to this: панять. Not in снять. Since both consonants й and н are weak, may be being both together the first "н", would disappear, if the root would be нйм-, and (за)[н]йм-у would become rightly (за)йм-у and (за)ня-ть would be OK. The problem? That this struggle between consonants is presented only when a stem that ends with... is followed by an ending beginning with... but not in any place of the word.
Perhaps просто it is only an exception between exceptions and nothing can be said, save: "Quod Principi placuit, legis habet vigorem" :thanks:

Yep. I believe that here formal rules only muddle the matter. The best way to learn conjugations of such problematic verbs is to make excersizes until you get used to them.

Yes, but if I can get some help of some rule... . In this case it seems not being such a rule :search: Really making clear why взять becomes возьму is quite a challenge and things like this. Both tools seem usefull, firstly learn what "there is", and then if possible understand why it is like this. Thank you.

занять - займу
понять - пойму
унять - уйму
перенять - перейму
принять - приму
отнять - отниму
донять - дониму
внять - вниму

The root here им originated from "иметь". Naturally this verb is one of the most irregular in many languages.

I think "взять-(возиму)-возьму" has the same origin. Maybe вынуть, сунуть too.

In conjugation, if prefix ends on consonant, the group of consonants with "й" (-тйм-, -зйм-, ) in the middle would be hard to pronounce. Epenthetical н helps to avoid it, as well as "й - ы" transformation.
занять - займу
понять - пойму
унять - уйму
перенять - перейму
принять - приму
отнять - отниму (also, отыму)
донять - дониму (actually, "дойму")
внять - вниму (actually, "войму")
Also, снять - сниму, сыму; изъять - изыму (no н in infinitive, no н in present-future paradigm); поднять - подниму, подыму.

In the form of infinitive н was inserted later, by analogy to forms in conjugation. Cf modern "обнять", archaic "объять", for example, the proverb "Нельзя объять необъятное".
So, when you see ня In stem, look on the prefix. If it ends on consonant, use ни, if on vocal, use и))

Thank you for your answers that I will study carefully. As for взять -> возьму it became completely clear following the rules given in the mentioned page. That's why I find (in an excess of optimism) strange that this case would not be resolved somehow. Thank you.