-- Implicit indexes of tuples (number<->string conversion)
do
  local function t2i(s)
    local i = 0
    for k = 1, #s do
      i = i * 256 + s:byte(k)
    end
    return i
  end

  local function i2t(i)
    local a = {0}
    if i < 256 then
      return string.char(i)
    elseif i > 1 then
      local k = math.ceil(math.log(i+.5)/math.log(256))
      while i > 0 do
        a[k] = i % 256
        i = math.floor(i / 256)
        k = k - 1
      end
    end
    return string.char(unpack(a))
  end

  return {
    t2i = t2i,
    i2t = i2t
  }
end