1. Maxwell Institute for Mathematical Sciences and School of Mathematics, University of Edinburgh, Edinburgh, EH9 3FD, UK.
2. Dipartimento di Matematica, Università degli Studi di Trento, 38123, Povo (Trento), Italy.
3. MathNeuro Team, Inria at Université Côte d’Azur, 06410, Biot, France, and Politecnico di Torino, 10129, Torino, Italy.