TLA in Pictures

Predicate-action diagrams, which are similar to standard state-transition diagrams, are precisely defined as formulas of TLA (the Temporal Logic of Actions). We explain how these diagrams can be used to describe aspects of a specification—and those descriptions then proved correct— even when the complete specification cannot be written as a diagram. We also use the diagrams to illustrate proofs. Keywords—Concurrency, specification, state-transition diagrams, temporal logic.