Among the issues raised by North Korea's third nuclear test, on Tuesday, is what it means for Iran's nuclear programme. It is sometimes assumed that Iran will benefit from North Korea's nuclear advances. There is also speculation Pyongyang's successful defiance of the major powers will embolden Iran to continue its own defiance.
Let us examine each of these theories, and consider how, from the US perspective, lessons learnt from one can apply to the other.
The first assumption contends that the well-documented cooperation between North Korea and Iran in ballistic missile development extends to the nuclear field. I have written before in these pages of how the link is not proven but that the circumstantial evidence is accumulating. A recent example is that when Iran and North Korea signed a science and technological cooperation agreement in Tehran last September, both the head of Iran's Atomic Energy Organisation and the defence minister were present.
If the two countries do share their experience in developing nuclear reactors and uranium enrichment capabilities, which both claim is for peaceful purposes, there is much that they can teach each other. Both are constructing reactors of a type in which the other has expertise. And neither can legitimately receive nuclear technical assistance anywhere else (except, in Iran's case, from Russia to operate the Bushehr power reactor).
If nuclear cooperation were to extend all the way, North Korea now has new test results it could add to the exchange. Some commentators even claim that Iran could thereby develop a nuclear weapon without testing itself, because North Korea would in effect be doing so on behalf of both countries, particularly if the third test turns out to have used highly enriched uranium (HEU). North Korea's previous tests were of plutonium devices, but the nation no longer produces plutonium and has shifted its emphasis to uranium enrichment, the backbone of Iran's nuclear programme.
Speculation about nuclear weapons cooperation, however, far exceeds the bounds of what can be deduced through proven facts. Moreover, it would be risky for both countries to cooperate in nuclear technology, such as test results that could not be justified on grounds of peaceful nuclear energy. Nuclear weapons cooperation would cross a redline and could be the trigger for military action against Iran.
Taking up the second assumption, Iran pays close attention to North Korea's programme and to how the major powers react to developments. There is a kind of kinship in being the two surviving members of George W Bush's "axis of evil". But Iran's interest in the North Korean case goes beyond a curiosity in how a friend is faring.
Iran noticed that North Korea was able to violate the Nuclear Non-Proliferation Treaty without serious penalty. When Saddam Hussein and Muammar Qaddafi were overthrown, Iranian leaders presumed that the Kim family wasn't attacked because, unlike the deposed dictators, they have nuclear weapons.
The supposed lesson is wrong, however. Despite many provocations over the years, North Korea has not been subject to a military attack by the US since the Korean War ended in 1953. Washington did not want to spark another war that would have left Seoul in flames.
The correct historical lesson is that North Korea was not under threat of invasion when they did not have nuclear weapons and they are not under threat of attack today when they have them. The reason then and now is the same: it is because North Korea's artillery and missiles hold Seoul hostage.
Iran's official response to the North Korean nuclear test was to tut-tut disapproval. After all, Iran calls for a world free of nuclear weapons, so it can hardly applaud an expansion of the nuclear club. Privately, however, regime insiders might find it hard to suppress a grin at the repeated times North Korea has managed to aggravate the United States. If North Korea can do it, Iran cannot help but expect that it could also survive international condemnation if it were to similarly choose to produce nuclear weapons. This, too, however, would be the wrong lesson for Iran to learn.
In North Korea's case, America's most concerned ally, the Republic of Korea, has adamantly opposed pre-emptive military strikes against the North. In Iran's case, the situation is the opposite: America's most concerned allies, Israel and Saudi Arabia, would be pleased if the US took care of the problem militarily.
As the US and its allies consider how to respond to Pyongyang's latest provocation, they will look to lessons for how the Iran case has been handled. There, although sanctions have not produced any policy change in Iran, they have had a devastating effect on the economy. Western powers may seek to apply to North Korea the same kind of unilateral financial sanctions.
Sanctions targeting North Korea's international financial connections could be effective in two ways. Firstly, for patronage and to sustain their lifestyle, the Kim family relies on profits from illicit trade. Freezing their accounts in foreign banks would directly punish the leadership. The freeze that was put on the regime's accounts in Macau's Banco Delta Asia in 2005 got their attention immediately. Secondly, targeting North Korea's financial and illicit trade ties would reduce its means of marketing nuclear wares. If Tuesday's test confirms North Korea is producing HEU, the US will want to ensure fissile material is not provided to non-state actors, because it can be used to make crude nuclear weapons.
The Banco Delta Asia story did not end so well, in that the financial pressure contributed to North Korea's decision to up the ante by conducting its first nuclear test. But with that genie already out of the bottle, and with North Korea seemingly intent on ignoring all entreaties to pursue a peaceful path, the risks may be judged worthwhile.
Mark Fitzpatrick is the director of the Non-Proliferation and Disarmament Program at the UK-based International Institute for Strategic Studies