* [Penn lambda calculator](http://www.ling.upenn.edu/lambda/) Pedagogical software developed by Lucas Champollion, Josh Tauberer and Maribel Romero.<p>
<!-- Haskell Curry had ideas that he felt were validated upon reading a 1924 paper by M. Schönfinkel "Uber die Bausteine der mathematischen Logik" which used combinators in a similar way to his own ideas. Haskell then wrote "An analysis of logical substitution" which appeared in the American Journal of Mathematics in 1929. -->
* [Penn lambda calculator](http://www.ling.upenn.edu/lambda/) Pedagogical software developed by Lucas Champollion, Josh Tauberer and Maribel Romero.<p>
<!-- Haskell Curry had ideas that he felt were validated upon reading a 1924 paper by M. Schönfinkel "Uber die Bausteine der mathematischen Logik" which used combinators in a similar way to his own ideas. Haskell then wrote "An analysis of logical substitution" which appeared in the American Journal of Mathematics in 1929. -->