Problem:
The workers operate three machines. Let's denote by \( A_{i} \) the events, that during the day the machine with number \( i \) will require attention, \( i=1,2,3 \). Express the following events through \( A_{i} \) : \( A \) - three machines have a defect during the day; \( B \)-at least one machine has a defect during the day; \( C \)-no machine has a defect during the day.