Updated customizing.md

Author: aadityanaik

customizing.md

@@ -161,7 +161,7 @@ The checker module is the way Code2Inv verifies if the predicted invariant is co
 
 Examples of the checker module can be found in the [`code2inv/prog_generator/checkers` directory](code2inv/prog_generator/checkers).
 
-There are two functions that must be present in the checker- `inv_checker` and `inv_solver`. `inv_checker` will take the verification condition file name, the invariant string (as produced taking the invariant grammar into account) and a list of `(variable_name, variable_value)` assignment pairs. `inv_checker` will assign the variables their values (any variable in the invariant not in the assignment pair is assigned the value of 1) and evaluate the invariant based on these values, which should either return true or false.
+There are two functions that must be present in the checker- `inv_checker` and `inv_solver`. `inv_checker` will take the verification condition file name, the invariant string (as produced taking the invariant grammar into account) and a counter-example given as a list of `(variable_name, variable_value)` assignment pairs. `inv_checker` will assign the variables their values (any variable in the invariant not in the assignment pair is assigned the value of 1) and evaluate the invariant based on these values, which should either return true or false.
 
 `inv_solver` will take the verification condition file name and the invariant string and check if the invariant is correct or not and return a list of 3 elements. The invariant will be checked over the precondition, the loop condition and the post condition in that order. For each check, if the invariant is correct and there is no counter example, the corresponding list element will be `None`. If there is a counter example, the corresponding list element will be a dictionary of counter example variables mapped to their values.