FAQ

## We have moved!

Our new web portal is at potassco.org.

### Where can I find information about the API of clingo series 4?

The Script API Reference contains a complete description of the Python API; the one for Lua is analogous.

### Where can I find information about the language of gringo series 4?

• The Potassco Guide contains a complete (informal) language description with many examples.
• The Abstract Gringo paper formally defines syntax and semantics of a large subset of the gringo language.
• The ASP-Core-2 standard, a subset of the language of gringo 4

### How do optimization statements work?

An optimization statement consists of a set of elements consisting of a tuple together with a condition. Whenever the condition of such an element is true wrt an answer set, its associated tuple contributes a value to a set. Hence, if two equal tuples have true conditions, then only one value is provided. Additionally, tuples can have levels attached with the binary connective @ after the first tuple element - its value.

#### Example

```1 { a; b }.
#minimize { 2,t:a; 2,t:b; 1,u:b; 2,v:b }.
```

Given answer set {a, b}, the values of tuples (2,t), (1,u), and (2,v) are summed up. Hence, the minimize constraint evaluates to 5. Note that the value of tuple (2,t) provided by the first and second element of the optimization constraint is counted only once.
Given (the optimal) answer set {a}, the only tuple is (2,t). Hence, the minimize constraint evaluates to 2.

### How to compute supported models?

gringo and clasp apply simplifications that may suppress supported models. In fact, clasp's option --supp-models only suppresses the unfounded set check.

Rather we suggest a program transformation that replaces each positive body literal 'a' with 'not not a'. For instance, 'p :- p' has the empty stable model, the program 'p :- not not p' has the additional stable model containing 'p' only.

### How to obtain clingo with Python support under MacOS X?

The binary of clingo version >=4.4 for MacOS X version >= 10.9 should work fine. Otherwise, please let us know.