The time required by this operation is never worse that proportional to the sum of the sizes of the trees. As a map operation it determines if two maps are defined on the same domain. In the worst-case the time required by this operation is proportional to the size of the smaller tree. This procedure traverses the tree in-order, applying action to each association. The associations are processed in increasing order of their keys.
Action is a procedure of two arguments which take the key and datum respectively of the association.