“…For rational relations, the problem becomes undecidable, see (Carayol and Löding, 2014, Theorem 17) (however, each rational relation has a uniformization by a rational function, see Sakarovitch (2009), which needs not be subsequential). (i) The introduction of this measure has triggered similar work on two-way transducers, see Bose et al (2018Bose et al ( , 2019.…”