Since it is impossible to determine a priori the spans that will be used to make up a discourse tree, we will associate with each span that could possibly become part of a tree a status, a type, promotion, and primary intention relation and let discourse and intentional constraints determine the valid discourse trees.
we want to determine from the set of n + n , 1 + n , 2 + : : : + 1 = nn + 1 =2 potential spans that pertain to a sequence of n discourse units, the subset that adheres to some constraints of rhetorical and intentional well-formedness.