Common pitfalls

local a = {}  // create an empty table
local b = a   // b refers to the same table as a
a.x <- 1      // b.x is now also 1
b.x <- 2      // a.x is changed to 2

local start_time = settings.get_start_time() // this call is executed BEFORE the savegame is loaded -> undefined

local factory_coalmine = null                // we can create the variable ...
function start()
{
       factory_coalmine = factory_x(40, 78)  // ... but we can initialize it safely only in a function
}