6Lewis W A. Economic development with unlimited sup- plies of labour [ J ]. Manchester School of Economics and Social Studies, 1954,22 (2) : 139 - 191.
7Fei J, Ranis G. Development of Labor Surplus Economy : Theory and Policy [ M ]. Richard D. Irwin, Homewood, IL, 1964.
8Jorgenson D W. Surplus Agricultural Labour and the Development of A Dual Economy [ J ]. Oxford Economic Papers, 1967,19 (3) :288 - 312.
9Todaro M P. A Model of Labor Migration and Urban Un- employment in Less Developed Countries [ J ]. American Economic Review, 1969,59 ( 1 ) : 138 - 148.