In standard DRT the salmon introduced in [3c] would provide a suitable and accessible antecedent for the pronoun in [3f], but in fact this resolution appears to be unavailable. SDRT explains this observation in terms of a discourse structural constraint known as the Right Frontier Constraint. This constraint is best illustrated by drawing a discourse structure graph like the one below. A horizontal arrow in this graph indicates a coordinating discourse relation (where neither relatum dominates the other), in this case Narration. A vertical arrow indicates a subordinating discourse relation (where a nucleus dominates a satellite), in this case Elaboration. 