Question about definite/estimate consequences

[Roland Kaminski]

Hi, clasp's model object has two member functions to inspect whether a literal is definite or estimated. I also want to offer this functionality via the clingo API.

As far as I can see, I only have to expose the following two functions:

struct Model {
  //! True if p is part of a definite answer.
  bool isDef(Literal p) const;
  //! True if p is part of the current estimate of consequences.
  bool isEst(Literal p) const;
};

Now, I was thinking to add a few more lines to the documentation. To see if I understood correctly, can you tell me whether the statements below are true.

1. not in cautious/brave enumeration mode
   1. isDef is the same as isTrue
   2. isEst is always false
2. in cautious/brave enumeration mode
   1. isDef and isEst partition the true literals into estimated and definite consequences

I am asking, because I want to write a bit more in the API docs.

[Roland Kaminski]

I implemented a first version in potassco/clingo#423.

[Benjamin Kaufmann]

To see if I understood correctly, can you tell me whether the statements below are true.

1. not in cautious/brave enumeration mode
   
   1. `isDef` is the same as `isTrue`

Yes.

   2. `isEst` is always false

I think in the current implementation this is true but strictly speaking, isEst is undefined in this case.

2. in cautious/brave enumeration mode
   
   1. `isDef` and `isEst` partition the true literals into estimated and definite consequences

Yes.

[Roland Kaminski]

I decided to go with a "tribool" in the API. I also documented what happens in the normal enumeration mode.

In hindsight, it would have been better to call Model Solution and maybe use contains instead of is_true/is_consequence because one can nicely combine the two.

def is_consequence(self, literal: int) -> Optional[bool]:
    """
    Check if the given program literal is a consequence.

    The function returns `True`, `False`, or `None` if the literal is a
    consequence, not a consequence, or it is not yet known whether it is a
    consequence, respectively.
  
    While enumerating cautious or brave consequences, there is partial
    information about which literals are consequences. The current state of
    a literal can be requested using this function. If this function is
    used during normal model enumeration, the function just returns whether
    a literal is true of false in the current model.
  
    Parameters
    ----------
    literal
        The given program literal.
  
    Returns
    -------                                                                                                                                                                            
    Whether the given program literal is a consequence.
    """

[Benjamin Kaufmann]

@rkaminsk Can we close this issue or is there something more to do?

[Roland Kaminski]

@rkaminsk Can we close this issue or is there something more to do?

We can close it.