12. The method of claim 7 wherein the at least one traversal is at least one post-order traversal.
7. The method of claim 1 where the step of comparing the at least one sub-expression of the input expression to the at least one element of the at least one set of input sub-expressions comprises the steps of: performing at least one traversal of both the at least one sub-expression of the input expression and at least one element of the at least one set of input sub-expressions, the traversal involving the visitation of at least one node; forming at least one representation of the at least one node visited on the at least one traversal; and comparing the at least one representation of the at least one sub-expression of the input expression to at least one representation of the at least one element of the set of input sub-expressions.