def create_grid(size=4):  # Fonction renvoyant une grille de taille size
    """
    Creates and returns a two-dimensional (size x size) square matrix.

    :param size: Size of the grid (default 4)
    :return: List with "size" elements, each of them a list of "size" elements filled with 0.
    """
    game_grid = []
    for i in range(0, size):
        game_grid.append(size*[0])
    return game_grid