`Notes`

`Notes`

```
```[1] This reads "an equivalent element" rather than "the same element" 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* is true) but not equal. See the LessThan Comparable requirements for a fuller discussion.) If you're using a total ordering (if you're using *strcmp* , for example, or if you're using ordinary arithmetic comparison on integers), then you can ignore this technical distinction: for a total ordering, equality and equivalence are the same.

[2] Note that the range *[first2, last2)* may contain a consecutive range of equivalent elements: there is no requirement that every element in the range be unique. In this case, *includes* will return *false* unless, for every element in *[first2, last2)*, a distinct equivalent element is also present in *[first1, last1)*. That is, if a certain value appears *n* times in *[first2, last2)* and *m* times in *[first1, last1)*, then *includes* will return *false* if *m < n*.