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in System and Software Verification book there is a claim: if I have 2 systems A and B As you see in those two images there are A and B systems have 4 states in both, and rA take two values T or F and, rB also take two values T or F, and turn take two values A or B. the synch Product will be : A * B * rA * rB * turn ====> 4 * 4 * 2 * 2 * 2 =128 states I summaries the description in those pictures The book gives claim that there are only 21 reachable states and that a state of the type (4,4,.....) is not among those 21. could you explain or show why they are only 21 and why (4,4,....) not reachable

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