According to equation (15.17), the value of a perpetual American put option is given by:
$V = \frac{K}{r} - \frac{S}{r} + \frac{S}{r} \cdot \frac{1}{1 - \frac{H}{S}}$
Substituting $H$ for $S$ in the equation, we get:
$V = \frac{K}{r} - \frac{H}{r} +
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