Hereditary substitutions for simple types (revised)
Chantal Keller and Thorsten Altenkirch. 2010. Hereditary substitutions for simple types, formalized.
In Proceedings of the third ACM SIGPLAN workshop on Mathematically structured functional programming (MSFP '10). ACM, New York, NY, USA, 3-10.
Chantal Keller. 2010. The decidability of the βη-equivalence using hereditary substitutions.
I tried to refactor the code in  and , to make it more "good-looking". Whether the result is really better than the original, is disputable. "There's no accounting for taste." :-)
Note.  is under GNU General Public License. Thus, the part of the code that is based on  is under GPL. On the other hand, the text of the paper  is not under GPL. Hence, the code that is directly based on  needn't be under GPL (and it is not).