S. Jafar Murtadha A'amilli has a research about the subject, but it is in Arabic. I don't have a research or a book in English or Urdu on the subject, but I can give a brief on it, and I hope it's enough to explain it.
Duties are divided into two parts:
1- A duty that has to be done: it is what you must do, such as daily prayer, fasting the month of Ramadan for the healthy person other than the traveller, and the hajj for the man who is able to do it.
2- A duty to choose: in which the person in charge is can choose between two or more acts, and it is mentioned in the Qur'an in more than one resource, such as:
a- Fasting for those who can fast with difficulty: They can choose between fasting and paying the ransom of iftar.
b- Atonement of the deliberate iftar in the month of Ramadan, where the person can choose either fasting two consecutive months, feeding sixty poor people, or freeing a slave.
c- Atonement for the violation of the oath, it is a choice between freeing a neck or feeding ten poor people.
There are similar duties mentioned in the hadiths, such as the choice in the third and fourth rak'ahs between the reading of Surat al-Hamad and the four revelations.
Like this, the fuqaha'a in the time of absence of Imam reached to a conclusion that the person has the choice on Friday between Friday prayer and noon prayer, because we know that one of them is required for sure.