Temporal Logic of Actions
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Temporal Logic of Actions (TLA) is a logic developed by Leslie Lamport, which combines temporal logic with a logic of actions. It is used to describe behaviours of concurrent programs.
Statements in temporal logic of the form [[A]_t], where A is an action and t contains a subset of the variables appearing in A. An action is an expression containing primed and non-primed variables, such as [x+x'*y=y']. The meaning of the non-primed variables is the variable's value in this state. The meaning of primed variables is the variable's value in the next state. The above expression means the value of x now, plus the value of x tomorrow times the value of y now, equals the value of y tomorrow.
The meaning of [[A]_t] is that either A is valid now, or the variables appearing in t do not change. This allows for stuttering steps, in which none of the program variables change their values.
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