On Understanding Data Abstraction, Revisited: http://www.cs.utexas.edu/~wcook/Drafts/2009/essay.pdf
CLU Reference Manual: http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-225.pdf
Semantics Engineering with Redex: https://mitpress.mit.edu/books/semantics-engineering-plt-redex
On Understanding Types, Data Abstraction, and Polymorphism: http://lucacardelli.name/Papers/OnUnderstanding.A4.pdf
Practical Foundations of Programming Languages: http://www.cs.cmu.edu/~rwh/plbook/book.pdf