Yongjian Li Jian Chen Xiaoqiang Cai Fengsheng Tu Optimal Manpower Planning with Temporal Labor and Contract Period Constraints. 350-359 2005 conf/aaim/2005 AAIM https://doi.org/10.1007/11496199_38 db/conf/aaim/aaim2005.html#LiCCT05