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.
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3.5 – Precedence

Operator precedence in Lua follows the table below, from the higher to the lower priority:

             not  - (unary)
             *   /
             +   -
             <   >   <=  >=  ~=  ==
All binary operators are left associative, except for `^´ (exponentiation) and `..´ (concatenation), which are right associative. Therefore, the following expressions on the left are equivalent to those on the right:
    a+i < b/2+1          <-->       (a+i) < ((b/2)+1)
    5+x^2*8              <-->       5+((x^2)*8)
    a < y and y <= z     <-->       (a < y) and (y <= z)
    -x^2                 <-->       -(x^2)
    x^y^z                <-->       x^(y^z)
When in doubt, always use explicit parentheses. It is easier than looking up in the manual and probably you will have the same doubt when you read the code again.