Planning is the activity of determining a list of actions that leads from the current state of the world to a desirable state of the world.
Actions change the state of the world.
Planning is the activity of determining a list of actions that leads from an undesirable state of the world to a desirable one.
Automated planning means that a computer performs this activity.
For this to work, the state of the world and the actions with their effects on the world must be formalized in a way that allows computers to reason about them.
The state of the art in automated planning is called \emph{classical planning}.
In classical planning, the state of the world is a set of nullary predicates called \emph{fluids}.
An action consists of a precondition and an effect.
The precondition is a set of fluids that must be included in the current state in order for an action to be executable.
The effect of an action is two sets of fluids, one that is added to the state and one that is deleted.
When the action is executed, the state is modified according to the action's effect.
A concise definition of classical planning is given by \citet{MuiseBM2016}.
