continue to last commit, fix naming confusion for MultiSet
continue to last commit, fix naming confusion for MultiSet

cuhkshenzhen/CUHKSZLib,alesiong/CUHKSZLib,cuhkshenzhen/CUHKSZLib,Yexiaoxing/CUHKSZLib,alesiong/CUHKSZLib,Yexiaoxing/CUHKSZLib,cuhkshenzhen/CUHKSZLib,alesiong/CUHKSZLib,Yexiaoxing/CUHKSZLib