"At times the mirror increases a thing’s value, at times denies it. Not everything that seems valuable above the mirror maintains its force when mirrored. The twin cities are not equal, because nothing that exists or happens in Valdrada is symmetrical: every face and gesture is answered, from the mirror, by a face and gesture inverted, point by point. The two Valdradas live for each other, their eyes interlocked; but there is no love between them."

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This is the city of Valdrada as described by Italo Calvino. The city inspired one large book encompassing two smaller books, each mirroring the other.