In the system, a ship arriving at a harbor is allocated a vacant berth that fits for the ship. If no such a berth available, the ship has to wait in the pool until a suitable berth is available. The system provides the following functions to allow the harbor master to control the movement of ships in and out of the harbor:

arrive: to register the arrival of a ship

dock: to register a ship docking in a berth

leave: to register a ship leaving a berth

We assume that all ships will have to arrive and be waiting (perhaps only notionally) in the pool before they can dock

consistent: Harbor Bool

consistent(h)

Define a predicate expression for the following constraints:

1. A ship cannot be in two different places (i.e., both the pool and a berth) at once

2. A ship can be docked in only one berth

3. A ship can only be in a berth it fits

is_docked: ShipHarbor Bool

is_docked(s,h)

Define a predicate expression for the following constraint:

1. There exists a berth that is occupied by the ship s.

Guard functions expressing preconditions for the generator functions which are partial. These functions are derived from the observer functions.

can_arrive: ShipHarbor Bool

can_arrive(s,h)

Define a predicate expression for the following constraint:

1. The ship s is in neither the waiting pool nor a dock

can_dock: ShipBerthHarbor Bool

can_dock(s,b,h)

Define predicate expressions for the following constraints:

1. The ship s is in the waiting pool.

2. The ship s is not docked.

3. The berth b is vacant.

4. The ship s fits in the berth b.

can_leave: ShipBerthHarbor Bool

can_leave(s,b,h)

Define predicate expressions for the following constraint:

1. The ship s is the one that occupies the berth b