public static async Task<(T ArgMin, R Min, long MinIndex, T ArgMax, R Max, long MaxIndex)> Extremum<T, R> (this ChannelReader<T> reader,
                                                                                                                Func<T, R> selector,
                                                                                                                IComparer<R> comparer,
                                                                                                                ChannelParallelOptions options)

using Amphisbaena;
using Amphisbaena.Linq;

...

int[] data = new int[] {1, 2, 3};

var extremum = await data
  .ToChannelReader()
  .Extremum(item => item);