Pasted

local dictionary = {}
 
local function insertWord(dict, word)
    local head, tail = word:upper():match('^(%a)(%a*)$')
    if not head then return false; end
    if not dict[head] then dict[head] = {}; end
    if tail == '' then
        dict[head][''] = true
        return true
    else
        return insertWord(dict[head], tail)
    end
end
 
insertWord(dictionary, 'BAG')