Chapter 6 (Enhancements of the bisimulation proof method): 

In the  first  diagram following definition 6.5.5, the weak transition
from Q should not have the "hat" (the label should  simply be \mu)
[thanks to Nils A. Danielsson]

Page 244, proof of Lemma 6.2.14. In the final diagram, in the process on
the right-hand side of the initial pair, the sum ("+") shoud be  a
parallel composition ("|") 
[thanks to Idriss Riouak]