In memory of Nadia Grygorivna Shestopalova

License

Authors retain copyright of their work and grant the journal the right of its first publication under the terms of the Creative Commons Attribution License 4.0 International (CC BY 4.0), that allows others to share the work with an acknowledgement of the work's authorship.

Authors are permitted to enter into additional non-exclusive agreements for the distribution of the published version of their work (for example, depositing it in institutional repositories or including it in collections), provided that the original publication in this journal is properly acknowledged.