Parallel algorithms are algorithm overloads. Each parallel algorithm overload has an additional template type parameter named ExecutionPolicy, which is the first template parameter. Additionally, each parallel algorithm overload has an additional function parameter of type ExecutionPolicy&&, which is the first function parameter. [ Note: Not all algorithms have parallel algorithm overloads. — end note ]
Unless otherwise specified, the semantics of ExecutionPolicy algorithm overloads are identical to their overloads without.
Parallel algorithms shall not participate in overload resolution unless is_execution_policy_v<decay_t<ExecutionPolicy>> is true.