... (almost¹

As we will see, sometimes the probability of something happening ``accidently'' turns out to be zero (See Section 3.), but the possibility must always be considered.

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... \AA.²

For completeness, we note here that the full three-dimensional arrangement is somewhat more complicated than implied here. It consists of multiple sets of planes at various spacings, with the spacing $d=2.34$ Å being the most prominent.

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... particles!.³

Once you accept this as experimental fact for all elementary particles, you can prove as a theorem that the same relation holds for the center of mass motion of any object composed of such particles. Thus, you can also use the same value of the constant for a baseball or yourself.

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....⁴

Because there is nothing in the experiment to add energy to the particles, they all do arrive with the same magnitude of momentum $p$, as the figure shows.

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