No globals:

local mt = getmetatable(_G) or {} function mt.__index (t, k)	if k ~= 'arg' then error('Tried to read nil global ' .. tostring(k), 2) end return nil end function mt.__newindex(t, k, v)	if k ~= 'arg' then error('Tried to write global ' .. tostring(k), 2) end rawset(t, k, v) end setmetatable(_G, mt)