avaloniaProject/Models/ItemsOperation.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace avaloniaPr.Models
{
    internal class ItemsOperation
    {
        public static List<string> Items = new List<string> { "Сумма", "Разность", "Умножение", "Деление" };
    }
}