let
  type Vector ~ array 3 of Integer;
  type Matrix ~ array 3 of Vector;

  proc putvector (v: Vector) ~
    let var i: Integer
    in
      begin
      put ('['); putint (v[0]);
      i := 1;
      while i < 3 do
        begin
        put (' '); putint (v[i]);
        i := i+1
        end;
      put (']')
      end;

  proc putmatrix (m: Matrix) ~
    let var i: Integer
    in
      begin
      i := 0;
      while i < 3 do
        begin
        putvector (m[i]);
        puteol ();
        i := i+1
        end
      end;

  func diagonal
          (m: Matrix): Vector ~
    [m[0][0], m[1][1], m[2][2]];

  var me: Matrix
    
in
  begin
  me := [[1,2,3], [4,5,6], [7,8,9]];
  putmatrix (me); puteol ();
  putvector (diagonal (me));
  puteol (); puteol ();
  me[1] := [10,11,12];
  me[1][1] := 22;
  putmatrix (me); puteol ()
  end