Magic Mirror

A long, long time ago, Chef found a pair of magic mirrors. Naturally, he decided to play around with them to test their capabilities. There are an infinite number of boxes arranged in a line. The boxes are numbered $1, 2, 3, \ldots$ from left to right. Initially, all of these boxes are colored **white**. First, Chef chose two integer positions $X_1$ and $X_2$ such that $1 \le X_1 \lt X_2$, and