A Third Sector in the Core-Periphery Model: Non-tradable Goods
Vasco Leite, Sofia Castro, João Correia da Silva
Annals of Regional Science, vol. 50, 2013, p. 71-108.

Portugal s Minho-Lima Region as a Tourist Destination: Tourism Operators Attitudes towards Its Management and Promotion
José Cadima Ribeiro, Laurentina Cruz Vareiro
Tourism Economics, vol. 16, 2010, p. 385-404.