uniqval

function uniqval(t1,t2)
  local ret = {}
  for k,v in pairs(t1) do
    ret[v]=true
  end
  for k,v in pairs(t2) do
    if ret[v] then
      ret[v] = nil
    else
      ret[v]=true
    end
  end
  function corr(t,k)
    local nk = next(t,k)
    if not nk then
      return
    else
      return nk,corr(t,nk)
    end
  end
  return {corr(ret,k)}
end