3.4-4 A library receives an archive of a painter from his heirs. The archive includes the painter’s works and those created by a friend. As the owner of the archive, can the library use all the works for an exhibition without any further ado?

No, for several reasons: the heirs still own the copyrights in the artist’s works as the copyrights were not assigned with the ownership acquired as a gift. If the library wants to use the works for an exhibition, it needs the consent of the heirs. The copyrights in the works of the artist’s friends were also not assigned to the library with the gift. To use these works, the library needs the consent of these authors (and/or other owners of rights, e.g. their heirs).