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We now present a formal language with which we can write tree descriptions. This is the language of *Dominance Constraints with Set Operators* as described in [DN00]. It has the following abstract syntax:

where variables denote nodes and . represents proper dominance and disjointness. The constraint is satisfied when the relationship that holds between and is one in . Thus is satisfied either when and are equal, or when they denote nodes in disjoint subtrees. We write instead of and generally omit braces when we can write a single symbol.

Consider again the scope ambiguity example:

It can be expressed as the following dominance constraint:

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Denys Duchier

Version 1.2.0 (20010221)