为了练习泛型集合随便写的段代码，望帮忙指出报错原因，谢谢


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;namespace collection_person
{    class NameComparer : IComparer<personmain>
    {
        public static NameComparer Default = new NameComparer();
        public int compare(personmain p1, personmain p2)
        {            return System.Collections.Comparer.Default.Compare(p1.Name, p2.Name);
        }        
    }
   
    class personmain:IComparable<personmain>
    
    {   
        public int CompareTo(personmain p)
        {
            return this.Age -p.Age;
        }
    
        private string _name;
        private int _age;        public personmain(string Name, int Age)
        {
            _name = Name;
            _age = Age;
        }        public string Name
        {
            get{return _name;}
        }        public int Age
        {
            get { return _age; }
        }        static void Main(string[] args)
        {
            personmain p1 = new personmain("zhangsan", 24);
            personmain p2 = new personmain("lisi", 39);
            personmain p3 = new personmain("wanger", 17);
            List<personmain> persons = new List<personmain>();
            persons.Add(p1);
            persons.Add(p2);
            persons.Add(p3);
            Console.WriteLine(persons[1].Name);            persons.Sort();
            foreach (personmain p in persons)
            {
                Console.WriteLine(p.Name);
            }
            persons.Sort(NameComparer.Default);
            foreach(personmain p in persons)
            {
                Console.WriteLine(p.Name);
            }
              
            
            //Console.Read();
        }
    }
}
错误信息是'collection_person.NameComparer' does not implement interface
member 'System.Collections.Generic.IComparer<collection_person.personmain>.Compare(collection_person.personmain, collection_person.personmain)' 谁能帮忙指出其中的错误呢，最好给个详细的更改，本人菜鸟一枚，先说声谢谢了～