using System;

using System.Linq;

using System.Threading.Tasks;

​

public class Program

{

    public static async Task Main()

    {

        var sequence_A = Enumerable.Range(1, 5).Select(i => $"A{i}").ToAsyncEnumerable();

        var sequence_B = Enumerable.Range(1, 5).Select(i => $"B{i}").ToAsyncEnumerable();

        var sequence_C = Enumerable.Range(1, 5).Select(i => $"C{i}").ToAsyncEnumerable();

        var merged = AsyncEnumerableEx.Merge(sequence_A, sequence_B, sequence_C);

        await foreach (var item in merged) Console.WriteLine(item);

    }

}