1. Hi there is an example in Chapter 4 Defining Basic Arithmetic Using ... subtitle.

     tbl1 = {"alpha", "beta", "gamma"}
     tbl2 = {"delta", "epsilon", "zeta"}
     tbl3 = {}
     mt = {}
    
     setmetatable(tbl1, mt)
     setmetatable(tbl2, mt)
     setmetatable(tbl3, mt)
    
     function mt.___add(a,b)
     local result = setmetatable({}, mt)
     -- Copy table a in first
     for i = 1, #a do
     table.insert(result, a[i])
     end
     -- Copy table b in second
     for i = 1, #b do
     table.insert(result, b[i])
     end
     return result
     end
    
     add_test = tbl1 + tbl2
    

    When i try to compile this example i get an error message like this:

    lua -e "io.stdout:setvbuf 'no'" "metatable.lua" lua: deneme.lua:23: attempt to perform arithmetic on global 'tbl1' (a table value) stack traceback: metatable.lua:23: in main chunk [C]: ? Exit code: 1

    Thanks. Very nice book. I wish you continued success.

    You have three underscores on ___add, and you only need two, i.e. __add.

    Thank you very much :)