namespace System.Linq
{
    public static class ParallelEnumerable
    {
        [Obsolete("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
        public static ParallelQuery<TResult>! Join<TOuter, TInner, TKey, TResult>(this ParallelQuery<TOuter>! outer, IEnumerable<TInner>! inner, Func<TOuter, TKey>! outerKeySelector, Func<TInner, TKey>! innerKeySelector, Func<TOuter, TInner, TResult>! resultSelector, IEqualityComparer<TKey>? comparer);
    }
}