Using constraint over reals

The abductive system allows real numbers domain constraints to be used in the abductive theory, and uses the library(clpr) module of SICStus for solving the constraints during abductive inference. A constraint in this domain is written as {Constraint}, where the grammar for Constraint can be found at the SICStus documentation ² and is included here for your reference:

$$\small \begin{array}{lll} Csontraint & ::= C & \\ & \mid C ... ...in}(Expr,Expr) & \\ & \mid {\tt max}(Expr,Expr) & \end{array}$$

For example, an action effect condition of buy can be encoded as a rule using a real domain constraint (the cost of an item is a positive real number):

initiates(buy(Item, Place), balance=B, T) :-
  sells(Place, Item, _Cost), holds(at(Place), T),
  holds(balance=B0, T), sells(Place, Item, Cost),                 
  {B = B0 - Cost}.