how many?
how many results of applying a rule?
- matching can produce 0, 1 or several dictionaries
- instantiation always produces exactly one result from each pattern and dictionary
- but two dictionaries may yield the same result
example
- datum is (1 2)
- pattern is (~a ~b)
- template (~b ~a)
- 3 matches (~a associated with (), (1), (1 2))
- but only 2 results: (1 2) and (2 1)