multiply-occurring vars
what happens when a variable occurs twice?
- given our definition of matching, answer is clear: must be matched to the same value in both places
- implementation in problem set uses dictionary merging
example
- (~ ~a ~ ~a ~) (youre repeating yourself)
- (~ ?a ?a ~) (youre stammering)
- (?x + ?x) (2 ?x)
- (?x / ?x) (1)