`Notes`

`Notes`

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```[1] Even this is not a completely precise description, because the ordering by which the input ranges are sorted is permitted to be a strict weak ordering that is not a total ordering: there might be values *x* and *y* that are equivalent (that is, neither *x < y* nor *y < x*) but not equal. See the LessThan Comparable requirements for a more complete discussion. The output range consists of those elements from *[first1, last1)* for which equivalent elements do not exist in *[first2, last2)*, and those elements from *[first2, last2)* for which equivalent elements do not exist in *[first1, last1)*. Specifically, suppose that the range *[first1, last1)* contains *m* elements that are equivalent to each other and the range *[first2, last2)* contains *n* elements from that equivalence class (where either *m* or *n* may be zero). If *m > n* then the output range contains the *lastm – n* of these elements elements from *[first1, last1)*, and if *m < n* then the output range contains the last *n – m* of these elements elements from *[first2, last2)*.