Waltz filtering uses the * structure* of the domain to help
reduce the number of possibilities to be considered in a search.
It applies to problems with the following features:

- The problem involves an assignment of labels to objects.
- Assignment of labels is
*locally ambiguous*: multiple labels are possible for an object. - An object can have only one label (
*self-consistency*). - There are
*constraints*among objects. - Correct sets of label assignments must satisfy all constraints:
*global consistency*.

The problem could be solved by search that exhaustively tries all combinations of labels, but this would be slow.