It is now common practice to use structured sets of features to describe syntactic structures, and to compare such structured sets by some form of unification. It is extremely tempting to try to encode disjunctive information within this framework; unfortunately, general unification of disjunctive structures is NP-complete, which is not a desirable property for the basic operation involved in comparing descriptions. We note that certain kinds of disjunctive specifications can be converted to conjunctive ones. This enables us to describe a restricted set of disjunctive phenomena without incurring the costs associated with general disjunctive unification.
['Allan Ramsay']
Disjunction without tears