The name 'Set' does not exist in the current context

wifimodel.cs

using PropertyChanged;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
using Template10.Mvvm;
using Template10.Services.NavigationService;
using Template10.Utils;
using Windows.UI;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

namespace Models
{
	[ImplementPropertyChanged]
	public class WiFiAccessPoint
	{
		string _SSID = default(string);
		public string SSID { get { return _SSID; } set { Set(ref _SSID, value); } }

	}
}