Apalache Manual

Authors: Igor Konnov, Jure Kukovec, Andrey Kuprianov, Shon Feder

Contact: {igor,jure,andrey,shon} at informal.systems

Apalache is a symbolic model checker for TLA+. (Still looking for a better tool name.) Our model checker is a recent alternative to TLC. Whereas TLC enumerates the states produced by the behaviors of a TLA+ specification, Apalache translates the verification problem to a set of logical constraints. These constraints are solved by an SMT solver, for instance, by Microsoft's Z3. That is, Apalache operates on formulas (i.e., symbolicly), not by enumerating states one by one (i.e., state enumeration).

Apalache is working under the following assumptions:

  1. As in TLC, all specification parameters are fixed and finite, i.e., the system state is initialized with integers, finite sets, and functions of finite domains and co-domains.
  2. As in TLC, all data structures evaluated during an execution are finite, e.g., a system specification cannot operate on the set of all integers.
  3. Only finite executions of bounded length are analyzed.