26 Algorithms library [algorithms]

26.3 Parallel algorithms [algorithms.parallel]

26.3.5 ExecutionPolicy algorithm overloads [algorithms.parallel.overloads]

Parallel algorithms are algorithm overloads.
Each parallel algorithm overload has an additional function parameter P of type T&& as the first function parameter, where T is the execution policy template parameter.
[Note 1: 
Not all algorithms have parallel algorithm overloads.
— end note]
Unless otherwise specified, the semantics of calling a parallel algorithm overload are identical to calling the corresponding algorithm overload without the parameter P, using all but the first argument.
Unless otherwise specified, the complexity requirements of a parallel algorithm overload are relaxed from the complexity requirements of the corresponding overload without the parameter P as follows: when the guarantee says “at most expr” or “exactly expr” and does not specify the number of assignments or swaps, and expr is not already expressed with notation, the complexity of the algorithm shall be .
A parallel algorithm with a template parameter named ExecutionPolicy shall not participate in overload resolution unless that template parameter satisfies execution-policy.