A flexible mathematical model for crew pairing optimization to generate n-day pairings considering the risk of COVID-19: a real case study. - Bahareh Shafipour-Omrani; Alireza Rashidi Komijan; Seyed Jafar Sadjadi; Kaveh Khalili Damghani; Vahidreza Ghezavati (Kybernetes, 2022)