Angular JS Provider is not working

app.provider('MyProvider', function () {
          var Name = 'Default';
          this.MyProviderMethod = function (s) {
              Name = s;
          };

          function Greeter(a) {
              this.greet = function () {
                  return Name + ',' + a;
              }
          };

          this.$get = function (a) {
              return new Greeter(a);
          };
      });

      app.config(function (MyProviderProvider) {
          MyProviderProvider.MyProviderMethod('Hi');
      });

      //app.controller('ControllerforProvider', ['MyProvider', function (MyProvider) {
      //    // this.DisplayName = MyProvider.greet('anvi');

      //    this.DisplayName = "fsss";
      //}]);


      app.controller('ControllerforProvider', ['MyProvider', function (MyProvider) {
          // this.DisplayName = MyProvider.greet('anvi');

          this.DisplayName = "h";
      }]);

<div ng-controller="ControllerforProvider as Contr">
             {{ Contr.DisplayName }}
         </div>