20 years of ordinal patterns: Perspectives and challenges Inmaculada Leyva, Johann H. Martínez, Cristina Masoller, Osvaldo A. Rosso and Massimiliano Zanin EPL, 138 3 (2022) 31001 Published online: 30 May 2022 DOI: 10.1209/0295-5075/ac6a72