9Merrill, Samuel Ⅲ; Grofman, Benlard, A Unified Theory of Voting: Directional and proximity Spatial Models, Cambridge University Press, 1999, ISBN: 9780521662222.
10Ng, Yew--Kwang, Welfare Economics: Towards a More Complete Analysis, Palgrave Macmillan, 2004, ISBN: 9780333971215.