 Complete the following phrase:  In the winter of 217, the warlord Liu Bei sent Zhang Fei, Ma Chao, Wu Lan 吳蘭 and others to garrison at Xiabian County 下辯縣; northwest of present-day Cheng County, Gansu in preparation for an invasion of Hanzhong Commandery, which Cao Cao had seized from the warlord Zhang Lu after the 