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Ordered Map "="
•Unlike a hashed map, there’s no need for ordered map "=" to search for the key, since the keys are already in sort order.
•If the key in the left map is equivalent to the corresponding key in the right map (equivalence being defined in terms of key "<"), then ordered map "=" compares the associated elements for equality. (This is the only time when element "=" is actually used.)
•Note that the key and element are both used to compute ordered map equality, but key equality is not used. (In fact key equality is never used in this API.)