1. Ashley-Rollman, M., Crary, K., Harper, R.: Solution to the poplmark Challenge in Twelf. Available electronically at http://fling-l.seas.upenn.edu/~plclub/mmm/ (2005)
2. Aydemir, B.E., Bohannon, A., Fairbairn, M., Foster, J.N., Pierce, B.C., Sewell, P., Vytiniotis, D., Washburn, G., Weirich, S., Zdancewic, S.: Mechanized metatheory for the masses: the poplmark challenge. In: Melham, T., Hurd, J. (eds.) Theorem Proving in Higher Order Logics: TPHOLs 2005, LNCS. Springer, New York (2005)
3. Barras, B.: Coq en Coq. Rapport de Recherche 3026. INRIA (1996)
4. Berghofer, S.: Extracting a normalization algorithm in Isabelle/HOL. In: Filliâtre, J.-C., Paulin, C., Werner, B. (eds.) Types for Proofs and Programs (TYPES 2004), Lecture Notes in Computer Science, vol. 3839. Springer, New York (2005)
5. Berghofer, S., Bulwahn, L., Haftmann, F.: Turning inductive into equational specifications. In: Berghofer, S., Nipkow, T., Urban, C., Wenzel, M. (eds.) 22nd International Conference on Theorem Proving in Higher Order Logics (TPHOLs 2009), Lecture Notes in Computer Science, vol. 5674, pp. 131–146. Springer, New York (2009)