@InProceedings{Pfe89,
    Author       = "Pfenning, F.",
    Year         = "1989",
    Title        = "{Elf: A Language for Logic Definition and Verified Metaprogramming}",
    BookTitle    = "{Proceedings of the 4th Annual Symposium on Logic in Computer Science}",
    Place        = "Pacific Grove, USA",
    Pages        = "313-322",
    Publisher    = "IEEE Computer Society Press",
    Comment      = "higher order"
}