It’s actually spelled “Bayes’ Theorem”. :-)

Note also that it’s more intuitive if you express it more symmetrically — like this:

P(E) * P(H | E) = P(H) * P(E | H)

Here’s how it works. There are two ways to compute the probability of both E and H occurring:

1. The chance that E occurs, multiplied by the chance that H occurs given E.
2. The chance that H occurs, multiplied by the chance that E occurs given H.

Dividing both sides by P(E) gives you the equation in your article.