I have been listening to some Italian songs lately and I have noticed a fact that I don't know if it's a rule or it's done only in the spoken language of the song to improve the flow of the song.
For example, in the song "Gli Anni" by 883, at some point it says:
Gli anni del "Tranquillo, siam qui noi"
Regarding what I know about Italian, shouldn't it be "Tranquillo siamo qui noi"?
Another example, in the song "Il bello d'esser brutti" by J-Ax, the title shouldn't be "Il bello d'essere brutti"?
Another example, and the last one, in the song "La canzone del sole" by Lucio Battisti, it says:
Ma quante braccia ti hanno stretto tu lo sai per diventar quel che sei
Shouldn't it be "per diventare quel che sei"?
I want to know if this is some kind of rule that I don't know and also applies for the written language, or if it's just a spoken trick to make it sound better. In any case, I would like you to explain me when we have to use this form or the another. Since I'm learning Italian and these kind of things confuse me a lot.