var intersectedList = listA.Intersect(listB, newButtonsListEquality());

1 List A :{1,5,9,6}
2 List B:{6,8,7,2,3}

  var bingji = ListA.Union(ListB, new ButtonsListEquality()).ToList();//并（全）集 

List A :{1,2,3,4,5,6}
List B:{5,6,7,8,9}

var chaji = ListA.Except(ListB, new ButtonsListEquality()).ToList();//差集

public class ButtonsListEquality : IEqualityComparer<SysButtons>
    {
        public bool Equals(SysButtons x, SysButtons y)
        {
            return x.Id == y.Id;
        }

        public int GetHashCode(SysButtons obj)
        {
            if (obj == null)
            {
                return 0;
            }
            else
            {
                return obj.ToString().GetHashCode();
            }
        }
    }