# Minimal Cut Set¶

The minimal cut set generation is a special mode where Kind 2 computes a minimal subset of the model elements (assumptions, guarantees, stateful equations, or node calls) whose no satisfaction leads to the violation of a property.

To enable minimal cut set generation, run

kind2 <lustre_file> --enable MCS


## Options¶

• --mcs_category {annotations|node_calls|contracts|equations|assertions} (default: annotations) – Consider only a specific category of elements, repeat option to consider multiple categories

• --mcs_only_main_node <bool> (default false) – Only elements of the main node are considered in the computation

• --mcs_all <bool> (default false) – Specify whether all the Minimal Cut Sets must be computed or just one

• --mcs_approximate <bool> (default true) – Compute a MCS which is minimal with respect to all the counterexamples of the same length that the first counterexample found. This solution can be considered an approximation of a global one. Ignored if --mcs_all is true

• --mcs_max_cardinality <int> (default -1) – Only search for MCSs of cardinality lower or equal to this parameter. If -1, all MCSs will be considered

• --mcs_per_property <bool> (default true) – If true, MCSs will be computed for each property separately

• --print_mcs <bool> (default true) – Print the minimal cut set computed

• --print_mcs_complement <bool> (default false) – Print the complement of the minimal cut set computed (this is equivalent to computing a Maximal Unsafe Abstraction)

• --print_mcs_legacy <bool> (default false) – Print the minimal cut set using the legacy format

• --print_mcs_counterexample <bool> (default false) – Print a counterexample for each MCS found (ignored if --print_mcs_legacy is true)

• --mcs_per_property <bool> (default true) – If true, MCSs will be computed for each property separately

## Example¶

Let’s consider the following Lustre code:

contract spec(x,y: real) returns(z: real);
let
weakly assume x = -y;
weakly assume x >= 0.0;
tel;

node main(x, y : real) returns (z : real);
(*@contract import spec(x,y) returns (z) ; *)
var P : bool;
let
z = x + y;
P = z = 0.0;
--%MAIN;
--%PROPERTY P;
tel;


If you are interesting in determining a minimal set of the weak assumptions of the contract fSpec whose no satisfaction leads to the violation of P, you can run this command:

kind2 <lustre_file> --enable MCS --mcs_category annotations


Note that --mcs_category annotations is not required since it is the default value.

The following minimal cut set is printed:

MCS (1 elements) for property P:
Node main
Assumption spec[l9c12].weakly_assume[l4c4][1] at position [l4c4]


In the example above, the weakly keywork is used to annotate the assumptions and guarantees to consider for the MCS computation (Kind2 will only try to remove these assumptions and guarantees, all the others will be kept).

Alternatively, if we want to compute a MCS over all the assumptions and guarantees, we can change the category to contracts:

kind2 <lustre_file> --enable MCS --mcs_category contracts