def get_neighbors_of(cell):
    """
    Return the neighbors of cell.
    """
    x = cell[0]
    y = cell[1]
    neighbors = set()
    for i in range(x-1, x+2):
        for j in range(y-1, y+2):
            if (i, j) != cell:
                neighbors.add((i, j))

    return neighbors