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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 ndtr(a):
 """ Returns the area under the Gaussian probability density function, integrated from minus infinity to x. See: https://docs.scipy.org/doc/scipy/reference/generated/scipy.special.ndtr.html#scipy.special.ndtr """

    sqrth = math.sqrt(2) / 2
    x = float(a) * sqrth
    z = abs(x)
    if z < sqrth:
        y = 0.5 + 0.5 * math.erf(x)
    else:
        y = 0.5 * math.erfc(z)
        if x > 0:
            y = 1 - y
    return y