Dubois, Catherine; Rouaix, François and Pierre Weis. "Extensional Polymorphism".

[POPL 1995] (1995) [ACM SIGACT-SIGPLAN] Proc. of the 22nd Annual ACM Symposium on Principles of Programming Languages, San Francisco, January 1995.  

Languages mentioned GCaml {1995} OCaml with polymorphic extensions