procedure setplot;
      begin
        x2:=x;
        y2:=y;
      end;

  procedure plot;
      begin
        line(x2,y2,x,y);
        setplot;
      end;

  procedure A(i : integer);forward;
  procedure B(i : integer);forward;
  procedure C(i : integer);forward;
  procedure D(i : integer);forward;

  procedure A;
  begin
    if i>0 then
        begin A(i-1);x:=x+h;y:=y-h;plot;
              B(i-1);x:=x + 2*h;plot;
              D(i-1);x:=x+h;y:=y+h;plot;
              A(i-1)
        end
  end;

  procedure B;
  begin
    if i>0 then
        begin B(i-1);x:=x-h;y:=y-h;plot;
              C(i-1);y:=y - 2*h;plot;
              A(i-1);x:=x+h;y:=y-h;plot;
              B(i-1)
        end
  end;

  procedure C;
  begin
    if i>0 then
        begin C(i-1);x:=x-h;y:=y+h;plot;
              D(i-1);x:=x - 2*h;plot;
              B(i-1);x:=x-h;y:=y-h;plot;
              C(i-1)
        end
  end;

  procedure D;
  begin
    if i>0 then
        begin D(i-1);x:=x+h;y:=y+h;plot;
              A(i-1);y:=y + 2*h;plot;
              C(i-1);x:=x-h;y:=y+h;plot;
              D(i-1)
        end
  end;


  PROCEDURE sierpin(n :INTEGER );
  begin
     opengraph;
     cleargraph;
     h := h0;
     x := 1000; y := maxint - 1;
     setplot;
     A(n);x:=x+h;y:=y-h;plot;
     B(n);x:=x-h;y:=y-h;plot;
     C(n);x:=x-h;y:=y+h;plot;
     D(n);x:=x+h;y:=y+h;plot
  end;