It says that a dependent element delta is universally preceded by its antecedent alpha in a category beta, which immediately dominates alpha and delta.
Recursion is built in by the fact that both alpha and delta can be a beta.
The variable-free formulation is possible thanks to Pied Piping. De Primaire Structuur . Empty Objects in Dutch. Ms., University of Groningen. Sentence-final Adverbials and Stress .