The author of a work is a natural person who has created the work. The author is presumed to be the person whose name, pseudonym or mark appears in the customary manner on the copies of the work, until proven to the contrary.
If several authors participated in the creation of a work a co-authors’ work is concerned.
If such a created work is an indivisible whole the co-authors have a joint copyright in it.
If two or more authors join their created works for the purpose of a joint use, each of them keeps the copyright in his/her own work.