//**************** Predicates *******************************************

At(object,location,time)
In(object,medium,time)

MediumAt(medium,location,time)

InCity(location,city)
Airport(location)

Truck(medium)
Airplane(medium)

MediumInCity(medium,city)

Successor(time,time)

//************************** RULES ***********************************


// Objects stay in place or are loaded 

// Only load planes/trucks at the same location 

// Objects stay in the truck/plane or are unloaded 

// Only unload a plane/truck at same location 

// A truck/plane is always in exactly in one location 

// Objects are at at most one location 

// Objects are in at most one medium 

// Objects are never both at a location and in a medium 

// Objects are always somewhere 

// A truck is in same city as its location

// An airplane is always at an airport


//***************** Heuristics (off by default) ***********************************


// H1: Once a package leaves a location, it never returns.

// H2: A package is never in any city other than its origin or destination cities.

// H3: Once a truck is loaded, it should immediately move.

// H4: A package never leaves its destination city.