“…The time-dependent variant of the OP is relatively new and has, to the best of our knowledge, only been studied in (Fomin and Lingas, 2002;Abbaspour and Samadzadegan, 2011;Garcia et al, 2013;Li et al, 2010;Li, 2011;Gavalas et al, 2014Gavalas et al, , 2015. Fomin and Lingas (2002) were the first authors to mention the TD-OP and state that it is NP-hard because the OP is NP-hard.…”