Defining 3 successive states

[Imran Meah]

I know we can define 2 state states machine (say states A and B) by using Next operator. My question is how do I define 3 or more states.

For example, read, process, write and I want the state to transition like this
read -> process -> write

[Apostolis Xekoukoulotakis]

If they are successive, why do you need to represent them with three states or two atomic actions instead of one?

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[Martin]

Hello Imran,

An action describes how the current state relates to the next. You could
add a variable status and use it to remember what you were about to do:


VARIABLE status

Init == status = "read"
Next == \/ status = "read" /\ status' = "process"
\/ status = "process" /\ status' = "write"

I am using strings to represent the different states because different
strings are always different (for arbitrary constants a,b I would need
to add an axiom a /= b ). The relation above doesn't do anything beyond
changing the status yet - anything more would go as an additional
conjunct for the status it is intended for.

hope this helps,
Martin