Reactor: Identifies the Realised_Molecule_Types and Realisable_Interaction_Types that are present in the simulation at each timestep.
Realised_Molecule_Type: Identifier for a Molecule_Type that is (or has been) realised as a Molecule in the Reactor. Once a particular Realised_Molecule_Type has existed in the Reactor sub-system, it remains present even if all of the Molecules of the Molecule_Type have been removed.
Molecule: A Molecule is an item that can exist in the Reactor sub-system. Molecules can be consumed or produced by interactions taking place in the Reactor according to the rules of the Interaction_Types defined in the Chemistry sub-system.
Realisable_Interaction_Type: Identifier for an Interaction_Type that is currently realisable in the Reactor. An Interaction_Type is realisable if its reactant Molecule_Types are present in the Reactor in sufficient numbers for at least one interaction to take place.