BTreeMatchingStrategy

Use a matching strategy appropriate for a set. I.e., match partition classes over key equality rather than individual keys.

This strategy ignores the multiplicity of keys, and only consider whether a key is included in the two trees at all. E.g., a single element from one tree will be considered a match for any positive number of elements with the same key in the other tree.

Use a matching strategy appropriate for a multiset. I.e., try to establish a one-to-one correspondence between elements from the two trees with equal keys.

This strategy keeps track of the multiplicity of each key, and matches every element from one tree with at most a single element with an equal key from the other tree. If a key has different multiplicities in the two trees, duplicate elements above the lesser multiplicity will not be considered matching.