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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 lognormcdf(x, mu, tau):
 """Log-normal cumulative density function"""

    x = np.atleast_1d(x)
    return np.array(
        [0.5 * (1 - flib.derf(-(np.sqrt(tau / 2)) * (np.log(y) - mu))) for y in x])