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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def hprewitt(image, mask=None):
    '''Find the horizontal edges of an image using the Prewitt transform

    image - image to process
    mask  - mask of relevant points

    We use the following kernel and return the absolute value of the
    result at each point:
     1   1   1
     0   0   0
    -1  -1  -1
    '''
    if mask is None:
        mask = np.ones(image.shape, bool)
    big_mask = binary_erosion(mask,
                              generate_binary_structure(2,2),
                              border_value = 0)
    result = np.abs(convolve(image, np.array([[ 1, 1, 1],
                                              [ 0, 0, 0],
                                              [-1,-1,-1]]).astype(float)/3.0))
    result[big_mask==False] = 0
    return result