Consider the following fauli$-$masking redundaincy scheme with voting. There are four

modules. Initially, three modules are operating concurrently, and one is a spare. When a

disagreement is detected between the three operating modules, the disagreeing module is

purged $($switched out$)$ and the spare is used to replace it$.$ After the spare has bsen switched

in$,$ a detected disagreement causes the disagreeing module and one of the good ones to be

purged, leaving a simplex system. State all your assumptions clearly. Construct and solve a

state$-$space reliability model for this system, assuming perfect coverage, switching, and

ving.