@Article{huet-residual, author = "{G\'erard} Huet", title = "Residual Theory in $\lambda$-Calculus: A Formal Development", journal = JFP, year = 1994, volume = 4, number = 3, pages = "371--394"}See Rasmussen's report The Church-Rosser Theorem in Isabelle: A Proof Porting Experiment.