/* Binary shared variable with test-and-set instruction  */

Process V[2]                               // two states of variable
Event fetchAndSetA0, fetchAndSetA1, loadA0 // access by A
Event fetchAndSetB0, fetchAndSetB1, loadB0 // access by B

V[0] <- fetchAndSetA0 V[1] + loadA0 V[0] +
        fetchAndSetB0 V[1] + loadB0 V[0]
V[1] <- fetchAndSetA1 V[1] + loadA0 V[0] +
        fetchAndSetB1 V[1] + loadB0 V[0]

// display V[0]

/* Two mutual-exclusion worker processes */

Process A, AWaiting, B, BWaiting
Event nonCriticalA, startCriticalA, finishCriticalA
Event nonCriticalB, startCriticalB, finishCriticalB

A        <- nonCriticalA AWaiting
AWaiting <- fetchAndSetA1 AWaiting +
            fetchAndSetA0 startCriticalA finishCriticalA loadA0 A

B        <- nonCriticalB BWaiting
BWaiting <- fetchAndSetB1 BWaiting +
            fetchAndSetB0 startCriticalB finishCriticalB loadB0 B

/* System */

Process System

System <- A*B*V[0]

//display ~System

/* Abstracted System */

Event varEvents, nonCriticals

varEvents = fetchAndSetA0 fetchAndSetA1 loadA0 fetchAndSetB0 fetchAndSetB1 loadB0
nonCriticals = nonCriticalA nonCriticalB

display ~(System - varEvents - nonCriticals)

/* Mutual exclusion property */

Process Mutex

Mutex <- startCriticalA finishCriticalA Mutex +
         startCriticalB finishCriticalB Mutex

print "(System - varEvents - nonCriticals) ==may Mutex ? "
print (may_eq((System - varEvents - nonCriticals),Mutex))
print "\n"