3Francois Perroux.Not Sur Le Notion De Pole Croissance. Economie Appliquée . 1955
4Williamson,Jeffrey G.Regional inequality and theprocess of national development:a description of the patterns. Economic Development and Cultural Change . 1965
5Johnson S C.Hierarchical clustering schemes. Psychometrika . 1967
6Ralhan P K.Structure and function of the agriforestry system incentral Himalaya. Agriculture Ecosystem and Environment . 1991