Building a sustainability in a two-echelon closed loop supply chains: a mathematical approach for permissible delay in payment and backloggingMohsen Lashgari, Seyed Jafar Sadjadi, Ata Allah Taleizadeh and Mahdi HeydariRAIRO-Oper. Res., 56 6 (2022) 4145-4180DOI: https://doi.org/10.1051/ro/2022127