Adding Nash 1950, Grief 1993 in econ (#615)

economics/README.md

@@ -11,3 +11,11 @@
 ## Open Source
 
 * [The Simple Economics of Open Source  (2000)](https://papers.ssrn.com/sol3/papers.cfm?abstract_id=224008) by Josh Lerner and Jean Tirole
+
+## Contract enforcement/principal-agent models
+
+* [Contract Enforceability and Economic Institutions in Early Trade: The Maghribi Traders' Coalition (1993)](https://web.stanford.edu/~avner/Greif_Papers/1993%20Greif%20AER%201993.pdf) by Avner Grief
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+## Game theory
+
+* [Two-person cooperative games (1950)](https://www.rand.org/content/dam/rand/pubs/papers/2005/P172.pdf) by John Forbes Nash