Mulligan, C. B., & Sala-i-Martin, X. (1999). Social security in theory and practice (II): Facts and political theories. National Bureau of Economic Research.
Lua i Stíl Chicago (17ú heag.)Mulligan, Casey B., agus Xavier Sala-i-Martin. Social Security in Theory and Practice (II): Facts and Political Theories. Cambridge: National Bureau of Economic Research, 1999.
Lua MLA (9ú heag.)Mulligan, Casey B., agus Xavier Sala-i-Martin. Social Security in Theory and Practice (II): Facts and Political Theories. National Bureau of Economic Research, 1999.
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