Пишу крестики нолики , как убрать повторное нажатие на одно и тоже место ?

uses graphABC,ABCObjects; 
var
  a: array [1..3, 1..3] of SquareABC; 
  yes, no: rectangleABC; 
  i, j, k, z, x, y: integer; 
  p1, p2: boolean; 
  nickname1, nickname2, s: string;
 
procedure yesno(x, y, mb: integer);
begin
  if (mb = 1) and (yes.PtInside(x, y) = true) then 
  begin
  end; 
  if (mb = 1) and (no.PtInside(x, y) = true) then 
  begin
    window.close; 
  end; 
end;
 
procedure winner1();
begin
  if ((a[1, 1].Text = 'X') and (a[1, 2].Text = 'X') and (a[1, 3].Text = 'X')) 
  or ((a[1, 1].Text = 'X') and (a[2, 1].Text = 'X') and (a[3, 1].Text = 'X')) 
  or ((a[1, 3].Text = 'X') and (a[2, 3].Text = 'X') and (a[3, 3].Text = 'X')) 
  or ((a[1, 2].Text = 'X') and (a[2, 2].Text = 'X') and (a[3, 2].Text = 'X')) 
  or ((a[2, 1].Text = 'X') and (a[2, 2].Text = 'X') and (a[2, 3].Text = 'X')) 
  or ((a[3, 1].Text = 'X') and (a[3, 2].Text = 'X') and (a[3, 3].Text = 'X')) 
  or ((a[1, 1].Text = 'X') and (a[2, 2].Text = 'X') and (a[3, 3].Text = 'X')) 
  or ((a[1, 3].Text = 'X') and (a[2, 2].Text = 'X') and (a[3, 1].Text = 'X')) then 
  begin
    SetFontSize(32); 
    sleep(1000); 
    window.clear; 
    TextOut(10, 10, 'Выиграл: '); 
    TextOut(400, 10, nickname1); 
    TextOut(10, 200, 'Сыграть еще?'); 
    yes := new RectangleABC(100, 350, 100, 30, clwhite); 
    no := new RectangleABC(400, 350, 100, 30, clwhite); 
    yes.Text := 'Да!'; 
    no.Text := 'Нет('; 
    Onmousedown := yesno; 
  end; 
end;
 
procedure winner2();
begin
  if ((a[1, 1].Text = 'O') and (a[1, 2].Text = 'O') and (a[1, 3].Text = 'O')) 
  or ((a[1, 1].Text = 'O') and (a[2, 1].Text = 'O') and (a[3, 1].Text = 'O')) 
  or ((a[1, 3].Text = 'O') and (a[2, 3].Text = 'O') and (a[3, 3].Text = 'O')) 
  or ((a[1, 2].Text = 'O') and (a[2, 2].Text = 'O') and (a[3, 2].Text = 'O')) 
  or ((a[2, 1].Text = 'O') and (a[2, 2].Text = 'O') and (a[2, 3].Text = 'O')) 
  or ((a[3, 1].Text = 'O') and (a[3, 2].Text = 'O') and (a[3, 3].Text = 'O')) 
  or ((a[1, 1].Text = 'O') and (a[2, 2].Text = 'O') and (a[3, 3].Text = 'O')) 
  or ((a[1, 3].Text = 'O') and (a[2, 2].Text = 'O') and (a[3, 1].Text = 'O')) then 
  begin
    SetFontSize(30); 
    sleep(1000); 
    window.Clear; 
    TextOut(10, 10, 'Выиграл: '); 
    TextOut(300, 10, nickname2); 
    TextOut(10, 200, 'Сыграть еще?'); 
    yes := new RectangleABC(100, 350, 100, 30, clwhite); 
    no := new RectangleABC(400, 350, 100, 30, clwhite); 
    yes.Text := 'Да!'; 
    no.Text := 'Нет('; 
    Onmousedown := yesno; 
  end; 
end;
 
procedure MouseMove1(x, y, mb: integer);
begin
  if (p1 = true) and (mb = 1) then 
  begin
    if a[1, 1].PtInside(x, y) = true then 
      a[1, 1].Text := 'X'; 
    if a[1, 2].PtInside(x, y) = true then 
      a[1, 2].Text := 'X'; 
    if a[1, 3].PtInside(x, y) = true then 
      a[1, 3].Text := 'X'; 
    if a[2, 1].PtInside(x, y) = true then 
      a[2, 1].Text := 'X'; 
    if a[2, 2].PtInside(x, y) = true then 
      a[2, 2].Text := 'X'; 
    if a[2, 3].PtInside(x, y) = true then 
      a[2, 3].Text := 'X'; 
    if a[3, 1].PtInside(x, y) = true then 
      a[3, 1].Text := 'X'; 
    if a[3, 2].PtInside(x, y) = true then 
      a[3, 2].Text := 'X'; 
    if a[3, 3].PtInside(x, y) = true then 
      a[3, 3].Text := 'X'; 
    p1 := false; 
    winner1(); 
  end; 
end;
 
procedure MouseMove2(x, y, mb: integer);
begin
  if (p2 = true) and (mb = 1) then 
  begin
    if a[1, 1].PtInside(x, y) = true then 
      a[1, 1].Text := 'O'; 
    if a[1, 2].PtInside(x, y) = true then 
      a[1, 2].Text := 'O'; 
    if a[1, 3].PtInside(x, y) = true then 
      a[1, 3].Text := 'O'; 
    if a[2, 1].PtInside(x, y) = true then 
      a[2, 1].Text := 'O'; 
    if a[2, 2].PtInside(x, y) = true then 
      a[2, 2].Text := 'O'; 
    if a[2, 3].PtInside(x, y) = true then 
      a[2, 3].Text := 'O'; 
    if a[3, 1].PtInside(x, y) = true then 
      a[3, 1].Text := 'O'; 
    if a[3, 2].PtInside(x, y) = true then 
      a[3, 2].Text := 'O'; 
    if a[3, 3].PtInside(x, y) = true then 
      a[3, 3].Text := 'O'; 
    p2 := false; 
    winner2(); 
  end; 
end;
 
begin
 
  SetFontSize(32); 
  writeln('Введите ник первого игрока: '); 
  readln(nickname1); 
  writeln(nickname1); 
  writeln('Введите ник второго игрока: '); 
  readln(nickname2);
  writeln(nickname2); 
  window.Clear; 
  x := 10; 
  y := 10; 
  k := -1; 
  z := 0; 
  SetFontSize(50); 
  for i := 1 to 3 do 
  begin
    for j := 1 to 3 do 
    begin
      a[i, j] := new SquareABC(x, y, 100, clwhite); 
      x := x + 100; 
    end; 
    x := 10; 
    y := y + 100; 
  end; 
  repeat
    p1 := true; 
    TextOut(380, 10, 'Ходит '); 
    TextOut(330, 80, nickname1); 
    while p1 = true do 
    begin
      OnMousedown := MouseMove1; 
    end; 
    p2 := true; 
    TextOut(380, 10, 'Ходит '); 
    TextOut(330, 80, nickname2); 
    while p2 = true do 
    begin
      OnMousedown := MouseMove2; 
    end; 
    k := k + 2; 
  until k >= 9; 
  if k >= 9 then 
  begin
    SetFontSize(30); 
    window.Clear; 
    TextOut(100, 200, 'Ничья! Начать заного?'); 
    yes := new RectangleABC(100, 350, 100, 30, clwhite); 
    no := new RectangleABC(400, 350, 100, 30, clwhite); 
    yes.Text := 'Да!'; 
    no.Text := 'Нет('; 
    Onmousedown := yesno; 
  end; 
end.