Research and Practice of Quantitative Models on The Freedom of Trade Based on AHP-FCE Method: Taking Major Countries in WTO as ExamplesQin Sishi, Tang Ji’an, Liu Feng, Shao Shuqian and Lu ShiyingE3S Web Conf., 214 (2020) 01048DOI: https://doi.org/10.1051/e3sconf/202021401048