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To implement this strategy in the case of an underpriced put option, the investor purchases the option and sells a call option with the same exercise price and maturity on the same underlying, thus creating a synthetic short position in the underlying. To eliminate the price risk, the investor sells another put and buys another call, but with a lower exercise price, thus creating a synthetic long position in the same underlying. Combining these transactions is equivalent to purchasing a bull call spread and, symetrically, a bear put spread. The investor uses only options, unlike the conversion or the reversal, which use the underlyings themselves or futures on the underlyings.