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### 1431. `is_permutation` must be more restrictive

Section: 27.6.14 [alg.is.permutation] Status: C++11 Submitter: INCITS Opened: 2010-08-25 Last modified: 2021-06-06

Priority: Not Prioritized

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Discussion:

Addresses US-120

`is_permutation` is underspecified for anything but the simple case where both ranges have the same value type and the comparison function is an equivalence relation.

[ Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. ]

Proposed resolution:

Restrict `is_permutation` to the case where it is well specified. See Appendix 1 - Additional Details