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 systems.
Statements in temporal logic are 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 today, plus the value of x tomorrow times the value of y today, 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.
