Quoting e-books
An e-book is usually the digitised version of a printed book, so correct quoting with page references is possible.
E-books, including a DOI (digital object identifier) are independent of their storage location and traceable, so you can use them for quoting.
Many e-books have an own ISBN which differs from the ISBN of the print version. They have the same quality concerning their content, so these e-books are also usable for quoting.
In which style you have to quote is defined by the particular faculty.
