Board Thread:Lua Help/@comment-8335270-20150302041119/@comment-3298582-20150302185903

@ : It's not neccessary, but  is a system variable and manipulating it is not required here.

@ :  changes from 1 to 3 in the first step (of your example), so you don't generate a sequence. only works on sequences. generates sequences if no argument for the position of new elements is given.