<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def prewitt(image, mask=None):
    '''Find the edge magnitude using the Prewitt transform

    image - image to process
    mask  - mask of relevant points

    Return the square root of the sum of squares of the horizontal
    and vertical Prewitt transforms.
    '''
    return np.sqrt(hprewitt(image,mask)**2 + vprewitt(image,mask)**2)