  The way in which discourse features express connections back to the previous
discourse has been described in the literature in terms of adjoining at the
right frontier of discourse structure. But this does not allow for discourse
features that express expectations about what is to come in the subsequent
discourse. After characterizing these expectations and their distribution in
text, we show how an approach that makes use of substitution as well as
adjoining on a suitably defined right frontier, can be used to both process
expectations and constrain discouse processing in general.
