Fairouz Kamareddine Qiao Haiyan Formalizing Strong Normalization Proofs of Explicit Substitution Calculi in ALF. 59-98 2003 30 J. Autom. Reasoning 1 db/journals/jar/jar30.html#KamareddineH03 http://dx.doi.org/10.1023/A:1022527914293