I have written a paper in mathematics and the journal which I sent my paper has accepted to publish it. I have two references in my article, and they are like:
1- "The proof of Akranov can be found with some additional information in the book of Mikhail Kirkhov [1]."
2- "We can prove this using the Prime Number Theorem (see [2] pp.138 for the conclusion from the PNT)..."
My question: Do I have to obtain written permissions from the authors of the books [1] and [2]? Is this a copyright issue?
No, you do not need to get permission to cite other works. Citing works is the way you give credit for existing ideas to the people who originally generated or made accessible those ideas. (and it's a bit troubling that you are asking this at this stage - have you not cited other work before at any level?)
You often do need to get permission for copying parts of works, such as figures, but where it is actually necessary is a legal issue that depends on a variety of circumstances. See for example: Is it necessary to obtain permissions for copying figures from published articles in your proposal/dissertation?
