I found some of the comments at http://stackoverflow.com/questions/5653678/union-types-and-intersection-types http://stackoverflow.com/questions/5653678/union-t

I found some of the comments at http://stackoverflow.com/questions/5653678/union-types-and-intersection-types http://stackoverflow.com/questions/5653678/union-types-and-i... helpful. If TAPL refers to "intersection types" then it's definitely a well-defined concept.