Another way to erase a bit is to swap it with another bit that reads 0. Swapping information between bits preserves information; to get back the original values of the bits, just swap them again. Before the swap, the first bit could read either 0 or 1; it has a bit’s worth of entropy. The second bit reads 0; it has no entropy. After the swap, the first bit reads 0; it has been restored to 0, or erased. The second bit reads 0 or 1; it has a bit’s worth of entropy—the same entropy that the first bit had before the swap. Swapping moves information and entropy from one place to another, but the
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