Transcriber’s Note:
The plain text version of this ebook includes complex mathematical
formulas. Some are simple in-line expressions like k = 1 - 1/μ^2. They
may include special notations such as x^y for x to the power of y, x_{y}
for x with a subscript of y, [=a] for an 'a' with a bar across the top,
[.a] for an 'a' with a dot over it, [..a] for an 'a' with two dots over
it. Others are more complex “ASCII Art” like this:
l l 2lc 2l
t₁ = ------ + ------ = -------- = --- β²
c - u c + u c² - u² c
Some are so complex that they must be rendered in the TeX mathematical
notation, enclosed between double dollar signs, like this:
$$ \beta = (1 - \frac {u^2}{c^2})^{-\frac{1}{2}} $$