It's not the same arithmetic taught at the Highland School in the 1940s.Comments welcome
However, it's a central component in the rules of the game that allow Arabs and Jews to manage alongside one another in the Middle East.
And by extension, how the rest of the world can accommodate itself to Muslims wrapped in religious fantasies similar to those that caused warfare among Christians in the Middle Ages.
There's a lesson in the details still unfolding within sight and sound of these fingers.
When the air is clear we can see the city of Amman from our balcony. And we hear the sound of gun fire associated with the crisis of the Temple Mount only a couple of miles to the south.
In a deal not said to be a deal, Israel has gotten back a guard from the Embassy in Jordan who killed an attacker, and Israel is removing metal detectors and cameras from entrances to the Temple Mount/al Aqsa.
All sides are saying it wasn't a quid pro quo, but none should believe them.
We're also thanking the Americans for their assistance, but that's no more than lip service. The real action involved security professionals from Israel and Jordan, operating with the blessings of King Abdullah and Prime Minister Netanyahu.
Donald Trump and his people are having enough trouble surviving in Washington. They're nowhere near Middle Eastern arithmetic.
We're saying that we'll replace the metal detectors with sophisticated cameras that know who the bad people are, can spot them in a crowd, and know when someone has a weapon hidden in their clothes.
That part of the deal is already causing problems with Palestinian religious authorities claiming absolute sovereignty over al Aqsa and everything around it.
One assessment is that Palestinians have lost the support of Jordan, Saudi Arabia, and Egypt, and have grasped the straw of Turkey, currently at odds with other Sunni governments, and seeking Sunni leadership by aligning itself with outcast Qatar and Iran.
Erdogan and Abbas, plus Israeli Muslim extremists are leading the incitement of whoever will follow them against Israel for alleged violations of the sacred mosque.
It may be too complex to follow, and to know how to respond if you're sitting in Fall River, Washington, or places nearby.
It ain't easy from Jerusalem, where we're hearing the wildest tales of what occurred on the Temple Mount, in Jordan, and what the Jews intend.
Truth among Muslims is likely to be even further from reality than with the current occupant of the White House.
No matter. More important is Middle Eastern arithmetic, and figuring how many people should die, and what other inconveniences and economic losses should be accepted in order to make a point?
We seek to protect ourselves from religious and nationalist fanatics among our neighbors, but some crazies slip through the cracks in the controls. Mistakes are made, as apparently they were by security people in Halamish.
Overall, Israel does as well as most western countries, and better than the US, in protecting its citizens from violence. Israel's murder rate is 1.36 per 100,000 population, while that of the US is 4.8. In both cases, the better neighborhoods and families are mostly free of danger. Violence is much greater than the national averages within the African American minority of the US and within the Arab minority of Israel.
And just as White Americans enjoy economic and social contacts with African Americans, so Israeli Jews are likely to count Arab Christians and Muslims among their friends and colleagues.
Not losing those positive contacts are among the considerations that enter into Middle Eastern arithmetic.
We also have to put up with the blather of Arabs and Jews who claim to know the way to Paradise.
Solving the problems of the Middle East, or living in absolute peace and harmony amidst Muslims (whether neighbors here or migrants to the US and Europe) is impossible. There may come a time when Muslims free themselves from fanatic dreams of ruling the world according to how they interpret Islamic religious law, but that's not in the cards for our generation, or most likely for our grandchildren.
Israel manages (as opposed to solving) the problem by a combination of security services, lots of snooping by various human and technological means, inconvenient check points, and highly trained personnel. Professionals respond to new threats, such as putting barrier posts in front of bus stops when it became an Arab fashion to drive a car into the people waiting for a bus.
Low level responses are best for dealing with individuals moved to express their spiritual motivations by killing Jews. When Arabs escalate, Israel responds with massive force. It's record of killing thousands in the West Bank and Gaza, as well as destroying neighborhoods, has worked reasonably well to dissuade many of those who may want to throw us into the sea.
However, escalation is costly for Israel. There'll be deaths and injuries to Jews, as well as an interruption in the benefits associated with Arabs working alongside Jews. We can replace Palestinian construction personnel with workers from China, Bulgaria, Romania and elsewhere, but the process will be expensive, cause delays, and fuel discontent among Palestinians deprived of their livelihood.
To be sure, and unfortunately, there will be tragedies. We cannot seal ourselves completely from danger. The point is to keep the casualties as few as possible.
The record, with few annual exceptions, are casualties from terror substantially lower than those from traffic accidents.
The arithmetic shows that it's safer to live alongside Arabs than alongside automobiles.
Alas, we cannot free ourselves from either.
How many lives to lose in response to violence for the prospects of how much safety, or peace and quiet, is the essence of Middle Eastern arithmetic.
Calculations are not simple. Experts are likely to quarrel at each point that a decision is required.
We're still arguing about the benefit of metal detectors alongside the Temple Mount as opposed to their capacity to provoke unrest among Muslims here and elsewhere.
There are no obvious answers in this arithmetic. 2+2 might be 4, or something else.
We're not sure that we've gotten through the worst of this crisis. Despite the removal of metal detectors and cameras, Muslims are demonstrating, throwing stones, attacking with knives, and demanding an elusive notion of greater victory.
If quiet returns it will not be complete, but hopefully it will last a reasonable time until the next crisis and uptick in violence.