@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.