An old Hasidic Jewish parable may offer some insight into the nuclear negotiating strategies of Iran and its western interlocutors: A man approaches his rebbe for advice, because his wife is complaining that their home is too small. The rebbe advises him to bring his hen into the house. Nonplussed but pious, the man obliges, and is soon back with further complaints. "Bring in your sheep," the rebbe advises, and subsequently tells him to bring in his donkey, and his cow, until the man arrives distraught with the news that his wife is about to leave.
"Now, take out the chicken," says the rabbi.
One reason for the positive atmospherics of the talks-about-talks in Istanbul last weekend was the fact that they avoided discussing any substantive compromise proposals. The follow-up talks scheduled for Baghdad on May 23, and the preparatory negotiations already underway between negotiator Helga Schmid and her Iranian counterpart Ali Bagheri, are more complicated precisely because they require the sides to put their cards on the table over what compromises they might accept.
Each side approaches negotiations still hoping to secure its own key goals, which is why each follows the advice of the proverbial rebbe and ratchets up pressure on the other in increments that can also be incrementally traded as concessions in order to secure its core objectives.
The most telling pressure being piled on Tehran is the raft of western sanctions targeting all who do business with Iran's energy and banking sectors. Iran's most important leverage comes through the behaviour that most alarms its western interlocutors - the steady expansion of its nuclear programme in a manner that gives it the means to build nuclear weapons even though it hasn't yet decided to do so.
Iran's core goal appears to be securing its right to enrich uranium to 3.5 per cent to power a nuclear reactor, as allowed by the Nuclear Non-Proliferation Treaty (NPT). Israel, France and until fairly recently even the US had demanded that Iran forego that right because even low-level enrichment for peaceful purposes leaves the means to create bomb fuel in Iran's hands.
Iran has now "brought the cow into the house" by using the fuel needs of a medical research reactor as a pretext to enrich uranium to 20 per cent - which considerably reduces the time required to reprocess it into bomb-grade material if it did decide to build a weapon.
Stopping 20 per cent enrichment has thus become the immediate goal of western powers. And statements by Iranian officials suggesting that such enrichment may no longer be necessary because the requisite fuel has been created suggest that it may be willing to play that element of its programme as a bargaining chip once serious negotiations get underway - but only in exchange for a significant reduction in sanctions.
Negotiations succeed when their agreed framework allows each side to see its core concerns addressed, despite deep differences.
For Tehran, the NPT holds out the prospect of western acceptance of its right to enrich uranium for peaceful purposes under international scrutiny. For western powers, the NPT provides the basis for demanding that Iran account for all of its nuclear work to the satisfaction of the International Atomic Energy Agency (IAEA), and also offers a framework for strengthening guarantees, through enhanced international monitoring, against any attempt by Iran to weaponise nuclear material.
The "reciprocity" principle also allows western powers to demand that Iran make an early substantial gesture establishing confidence in its intentions, while giving Tehran a basis to demand substantive concessions from western powers in exchange.
It's not hard to predict that the Schmid-Bagheri talks next month will focus initially on finding a formula for tying an Iranian freeze on 20 per cent enrichment to an easing of sanctions. Of course that doesn't resolve the wider dispute; it would be envisaged as a confidence-building step.
But even getting that much done will be politically tricky. Israel's Prime Minister Benjamin Netanyahu didn't waste a moment before denouncing the Istanbul talks as having given Iran a "freebie", allowing it five more weeks of unimpeded uranium enrichment. This is simply posturing: Mr Netanyahu knew the talks were never going to halt Iranian enrichment of uranium; that demand wasn't even on the table.
The Israeli leader's comments are instead aimed at rousing his considerable base of support on Capitol Hill to restrain President Barack Obama from making the compromises required for a diplomatic solution, which would have to involve Iran exercising its NPT right to enrich uranium once it had satisfied IAEA concerns. Israel and its more hawkish friends oppose any deal that leaves Iran enriching uranium, and they fear that diplomacy will mute the drums of war.
Although a diplomatic "solution" to the Iran nuclear standoff remains years away, a diplomatic process may be getting underway that could avert confrontation through reciprocal measures to ease tensions. It's inevitably going to be a protracted process that drags beyond November's US presidential elections and a political season that militates against compromise. Next month's French election could ease the path to compromise, however, if as expected it removes from the equation President Nicolas Sarkozy and his hardline on the question of uranium enrichment in Iran.
Will diplomacy succeed? Perhaps. After all, the key measure of success in diplomacy is the prevention of war. And this week's fall in the price of global oil futures suggests that the commodity markets most sensitive to the prospects of war and peace are encouraged by what they've seen in Istanbul.
Tony Karon is an analyst based in New York
On Twitter: @TonyKaron