Andrea Asperti Juliusz Chroboczek Safe Operators: Brackets Closed Forever Optimizing Optimal lambda-Calculus Implementations. 437-468 1997 8 Appl. Algebra Eng. Commun. Comput. 6 http://link.springer.de/link/service/journals/00200/bibs/7008006/70080437.htm db/journals/aaecc/aaecc8.html#AspertiC97