1. INRIA/Centre de mathématiques appliquées, École Polytechnique, Université Paris-Saclay, Route de Saclay, 91128 Palaiseau, France. E-mail: lucas.chesnel@inria.fr
2. Saint-Petersburg State University, Universitetskaya nab., 7–9, St. Petersburg, 199034, Russia
3. Institute of Problems of Mechanical Engineering RAS, V.O., Bolshoi pr., 61, St. Petersburg, 199178, Russia. E-mail: srgnazarov@yahoo.co.uk
4. Department of Mathematics and Statistics, University of Helsinki, P.O.Box 68, FI-00014 Helsinki, Finland. E-mail: jari.taskinen@helsinki.fi