Wendy Verbruggen Edsko de Vries Arthur Hughes Polytypic programming in COQ. 49-60 2008 ICFP-WGP http://doi.acm.org/10.1145/1411318.1411326 conf/icfp/2008wgp db/conf/icfp/wgp2008.html#VerbruggenVH08