Can someone explain Anonymous methods to me?

type
  TAnonFunc = reference to procedure;
  TForm2 = class(TForm)
    Memo1: TMemo;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    F1 : TAnonFunc;
    F2 : TAnonFunc;
  end;

procedure TForm2.Button1Click(Sender: TObject);
var
  a : Integer;
begin
  a := 1;

  F1 := procedure
  begin
    a := a + 1;
  end;

  F2 := procedure
  begin
    Memo1.Lines.Add(IntToStr(a));
  end;
end;

procedure TForm2.Button2Click(Sender: TObject);
begin
  F1;
end;

procedure TForm2.Button3Click(Sender: TObject);
begin
  F2;
end;

type
  TDisplayProc = TProc<TCanvas>;

type
  TFrmExample3 = class(TForm)
    pbxMain: TPaintBox;
    trkZoom: TTrackBar;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure pbxMainClick(Sender: TObject);
    procedure pbxMainMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
    procedure pbxMainPaint(Sender: TObject);
    procedure trkZoomChange(Sender: TObject);
  private
    FDisplayList: TList<TDisplayProc>;
    FMouseX: Integer;
    FMouseY: Integer;
    FZoom: Extended;
    procedure SetZoom(const Value: Extended);
  protected
    procedure CreateCircle(X, Y: Integer);
    procedure CreateRectangle(X, Y: Integer);
    function MakeRect(X, Y, R: Integer): TRect;
  public
    property Zoom: Extended read FZoom write SetZoom;
  end;

implementation

{$R *.dfm}

procedure TFrmExample3.PaintBox1Paint(Sender: TObject);
var
  displayProc: TDisplayProc;
begin
  for displayProc in FDisplayList do
    displayProc((Sender as TPaintBox).Canvas);
end;

procedure TFrmExample3.CreateCircle(X, Y: Integer);
begin
  FDisplayList.Add(
    procedure (Canvas: TCanvas)
    begin
      Canvas.Brush.Color := clYellow;
      Canvas.Ellipse(MakeRect(X, Y, 20));
    end
  );
end;

procedure TFrmExample3.CreateRectangle(X, Y: Integer);
begin
  FDisplayList.Add(
    procedure (Canvas: TCanvas)
    begin
      Canvas.Brush.Color := clBlue;
      Canvas.FillRect(MakeRect(X, Y, 20));
    end
  );
end;

procedure TFrmExample3.FormCreate(Sender: TObject);
begin
  FDisplayList := TList<TDisplayProc>.Create;
end;

procedure TFrmExample3.FormDestroy(Sender: TObject);
begin
  FreeAndNil(FDisplayList);
end;

function TFrmExample3.MakeRect(X, Y, R: Integer): TRect;
begin
  Result := Rect(Round(Zoom*(X - R)), Round(Zoom*(Y - R)), Round(Zoom*(X + R)), Round(Zoom*(Y + R)));
end;

procedure TFrmExample3.pbxMainClick(Sender: TObject);
begin
  case Random(2) of
    0: CreateRectangle(Round(FMouseX/Zoom), Round(FMouseY/Zoom));
    1: CreateCircle(Round(FMouseX/Zoom), Round(FMouseY/Zoom));
  end;
  pbxMain.Invalidate;
end;

procedure TFrmExample3.pbxMainMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
  FMouseX := X;
  FMouseY := Y;
end;

procedure TFrmExample4.SetZoom(const Value: Extended);
begin
  FZoom := Value;
  trkZoom.Position := Round(2*(FZoom - 1));
end;

procedure TFrmExample4.trkZoomChange(Sender: TObject);
begin
  Zoom := 0.5*(Sender as TTrackBar).Position + 1;
  pbxMain.Invalidate;
end;

filter(isOdd, [1, 2, 3, 5, 6, 9, 10]) --> [1, 3, 5, 9]