do
    local function lookup_memoized (val, memoized)
        if memoized[val] == nil then
            if type(val) == "table" then
                memoized[val] = {}
                memoizing_deepcopy (val, memoized, memoized[val])
            else
                return val
            end
        end
        return memoized[val]
    end

    function memoizing_deepcopy (src, memoized, res)
        local memoized = memoized or {}
        local res = res or {}
        for k, v in pairs(src) do
            if k ~= memoizing_deepcopy and v ~= memoizing_deepcopy then
                local nk = lookup_memoized (k, memoized)
                local nv = lookup_memoized (v, memoized)
                res[nk] = nv
            end
        end
        return res
    end
end