Preprocessing in APALACHE

Before translating a specification into SMT, apalache performs a number of preprocessing steps:

  • Inliner:
    • replaces every call to a user-defined operator with the operator's body
    • replaces every call to a let-in defined operator of arity at least 1 with the operator's body
  • PrimingPass: adds primes to variables in Init and ConstInit (required by TransitionPass)
  • VCGen: extracts verification conditions from the invariant candidate.
  • Desugarer: removes syntactic sugar like short-hand expressions in EXCEPT.
  • Normalizer: rewrites all expressions in negation-normal form.
  • Keramelizer: translates TLA+ expressions into the kernel language KerA.
  • ExprOptimizer: statically computes select expressions (e.g. record field access from a known record)
  • ConstSimplifier: propagates constants


Keramelizer rewrites TLA+ expressions into KerA. For many TLA+ expressions this translation is clear, however, some expressions cannot be easily translated. Below we discuss such expressions and the decisions that we have made.


  • Leslie Lamport. Specifying Systems: The TLA+ Language and Tools for Hardware and Software Engineers. Addison-Wesley Professional, 2004.