$($a$)$ For three$-$state devices, write an expression for the reliability of a low$-$level re$-$dundant system as the system reliability with respect to a short minus the system probability of an open. Show that this is equivalent to Eq$.(5\mathrm{.}22).$

$($b$)$ Repeat for a high$-$level redundant system by writing an expression for the sys$-$tem reliability with respect to an open minus the system probability of a short. Show that this expression is equivalent to Eq$.(5\mathrm{.}23)$