This first edition was written for Lua 5.0. While still largely relevant for later versions, there are some differences.
The fourth edition targets Lua 5.3 and is available at Amazon and other bookstores.
By buying the book, you also help to support the Lua project.

3.1 – Arithmetic Operators

Lua supports the usual arithmetic operators: the binary `+´ (addition), `-´ (subtraction), `*´ (multiplication), `/´ (division), and the unary `-´ (negation). All of them operate on real numbers.

Lua also offers partial support for `^´ (exponentiation). One of the design goals of Lua is to have a tiny core. An exponentiation operation (implemented through the pow function in C) would mean that we should always need to link Lua with the C mathematical library. To avoid this need, the core of Lua offers only the syntax for the `^´ binary operator, which has the higher precedence among all operations. The mathematical library (which is standard, but not part of the Lua core) gives to this operator its expected meaning.