1. Archives
2. DH: David Hawkins Papers, University of Colorado at Boulder Libraries, Archives Dept.
3. HS: Herbert Simon Collection, Carnegie Mellon University Archives, Pittsburgh, PA.
4. Paul A. Samuelson Papers, David M. Rubenstein Rare Book and Manuscript Library, Duke University. Durham, NC.
5. Piero Sraffa Papers, Wren Library, Trinity College, Cambridge, UK.