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 $*\_t$, 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 $x+x\text{'}*y=y\text{'}$. 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 $*\_t$ 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.

See also

• Temporal logic

External link

• TLA – The Temporal Logic of Actions

Formal methods | Temporale Logik der Aktionen