The paper establishes an equivalence between pure point diffraction and
certain types of model sets, called inter model sets, in the context of
substitution point sets and substitution tilings. The key ingredients are a new
type of coincidence condition in substitution point sets, which we call
algebraic coincidence, and the use of a recent characterization of model sets
through dynamical systems associated with the point sets or tilings.Comment: 29pages; revised version with update