Hanus, Michael Programming Logics, MPI for Informatics, Max Planck Society;
https://rdcu.be/dsZpW (Publisher version)
Hanus, M., & Josephs, B. (1993). A Debugging Model for Functional Logic Programs. In M. Bruynooghe, & J. Penjam (Eds.), Proceedings of the 5th International Symposium on Programming Language Implementation and Logic Programming (PLILP-93) (pp. 28-43). Berlin, Germany: Springer.