A communicating class is closed if the probability of leaving the class is zero, namely if i is in C but j is not, then j is not accessible from i.
Läviv klass on kinnine, kui klassist lahkumise tõenäosus (probability of leaving the class) on null: kui olek i asub lävivas klassis C, kuid olek j mitte, siis olek j ei ole kättesaadav olekust i.