  In this project, we have extended previous work on the formalization of the
process algebra CCS in HOL4. We have added full supports on weak bisimulation
equivalence and observation congruence (rooted weak equivalence), with related
definitions, theorems and algebraic laws. Some deep lemmas were also formally
proved in this project, including Deng Lemma, Hennessy Lemma and several
versions of the "Coarsest congruence contained in weak equivalence". For the
last theorem, we have proved the full version (without any assumption) based on
ordinals.
