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As of version 1.3.5, ProB supports TLA+.

Using ProB for Animation and Model Checking of TLA+ specifications

ProB uses the translator TLA2B, which translates the non temporal part of a TLA+ module to a B machine. To use ProB for TLA you have to download the from Unzip the Zip file and copy the TLA2B.jar to the 'lib' folder of the ProB installation directory ('../ProB/lib/'). When you then open a TLA+ module ProTLA generates the translated B machine in the same folder and loads it in the background. If there is a valid translation you can animate and model check the TLA+ specification. There are many working examples in the '../ProB/Examples/TLA+/'-directory.


The parser and semantic analyzer SANY serves as the front end of TLA2B. It was written by Jean-Charles Grégoire and David Jefferson and is also the front end of the model checker TLC. After parsing there is type checking phase, in which types of variables and constants are inferred. So there is no need to especially declare types in a invariant clause (in the manner of the B method). Moreover it checks if a TLA+ module is translatable (see Limitations of Translation).

To tell TLA2B the name of a specification of a TLA+ module you can use a configuration file, just like for TLC. The configuration file must have the same name as the name of the module and the filename extension 'cfg'. The configuration file parser is the same as for TLC so you can look up the syntax in the 'Specifying Systems'-book (Leslie Lamport). If there is no configuration file available TLA2B looks for a TLA+ definition named 'Spec' or alternatively for a 'Init' and a 'Next' definition describing the initial state and the next state relation. Besides that in the configuration file you can give a constant a value but this is not mandatory, in contrast to TLC. Otherwise ProTLA lets you choose during the animation process a value for the constant which satisfy the assumptions under the ASSUME clause. TLA2B supports furthermore overriding of a constant or definition by another definition in the configuration file.

Supported TLA+ syntax


P /\ Q                       conjunction
P \/ Q                       disjunction
~ or \lnot or \neg           negation
=>                           implication
<=> or \equiv                equivalence
BOOLEAN                      set containing TRUE and FALSE
\A x \in S : P               universal quantification
\A x : P
\E x \in S : P               existential quantification
\E x : P


e = f                        equality
e # f or e /= f              inequality 


{d, e}                       set consisting of elements d, e
{x \in S : P}                set of elements x in S satisfying p
{e : x \in S}                set of elements e such that x in S
e \in S                      element of
e \notin S                   not element of
S \cup T or S \union T       set union
S \cap T or S \intersect     set intersection
S \subseteq T                equality or subset of
S \ t                        set difference
SUBSET S                     set of subsets of S
UNION S                      union of all elements of S


f[e]                         function application
DOMAIN f                     domain of function f
[x \in S |-> e]              function f such that f[x] = e for x in S
[S -> T]                     Set of functions f with f[x] in T for x in S
[f EXCEPT ![e] = d]          the function equal to f except f[e] = d

Records                         the id-field of record r
[id_1|->e_1,...,id_n|->e_n]  construct a record with given field names and values
[id_1:S_1,...,id_n:S_n]      set of records with given fields and field types
[r EXCEPT !.id = e]          the record equal to r except = e

Strings and Numbers

"abc"                        a string
STRING                       set of a strings
123                          a number

Miscellaneous constructs

IF P THEN e_1 ELSE e_2 CASE P_1 -> e_1 [] ... [] P_n ->e_n CASE P_1 -> e_1 [] ... [] P_n ->e_n [] OTHER -> e LET d_1 == e_1 ... d_n == e_n IN e

Action Operators

v' the value of variable v in the next state (only variables are able to be primed) UNCHANGED v v'=v UNCHANGED <<v_1, v_2>> v_1'=v_1 /\ v_2=v_2 (the restriction of tuples is not relevant for the unchanged operator)

Supported standard modules


x + y addition x - y difference x * y multiplication x \div y division x % y remainder of division x ^ y exponentiation x > y greater than x < y less than x \geq y greater than or equal x \leq y less than or equal x .. y set of numbers from x to y Nat set of natural numbers


-x unary minus Int set of integers


SubSeq(s,m,n) subsequence of s from component m to n Append(s, e) appending e to sequence s Len(s) length of sequence s Seq(s) set of sequences s_1 \o s_2 or s_1 \circ s_2 concatenation of s_1 and s_2 Head(s) Tail(s)


Cardinality(S) IsFiniteSet(S) (ProTLA can not handle an infinite set as argument)

typical structure of a TLA+ module

MODULE m ----

EXTENDS m_1, m_2 CONSTANTS c_1, c_2 ASSUME c_1 = ... VARIABLES v_1, v_2 foo == ... Init == ... Next == ... Spec == ...


Temporal formulas and unused definitions are ignored by TLA2B (they are also ignored by the type inference algorithm).

Limitations of the translation

  • due to the strict type system of the B method there are several restrictions to TLA+ modules.
- the elements of a set must have the same type (domain and range of a function are sets)
- to compare records they must have the same fields in the same order and corresponding types of the fields must have the same types
- TLA+ tuple are translated as sequences in B, hence all components of the tuple must have the same type
  • there is no counterpart to the TLA+ choose operator in the B method
  • TLA2B do not support 2nd-order operators, i.e. operators that take a operator with arguments as argument (e.g.: foo(bar(_),p))

Naming conflicts

reserved B keywords: left, right, max, min, succ, pred, dom, ran, fnc, rel, id, card, POW, POW1, FIN, FIN1,

	size, rev, first, last, front, tail, conc, struct, rec, tree, btree, skip, ANY, WHERE, END, BE, VAR, ASSERT;

TLA+ Actions