| : | States of telephone instruments dialer & receiver. |
| : | States of transferring machines of first main exchange. |
| : | States of transferring machines of second main exchange. |
| : | State of radar. |
| : |
|
| : | Negation of. |
| : | Conjunction, disjunction respectively. |
| : | Reliability of the ith component of considered system corresponding to system state. |
| : | Reliability of the system as a whole. |
| : | Reliability functions, in case, failures follow Weibull, exponential time distribution, respectively. |