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johnynek/gist:8850549

Created February 6, 2014 19:05
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You can swap with only two registers if they point to elements of a group:
a = a + b
b = a - b
a = a - b
proof:
a1 = a + b
b1 = a1 - b = a
a2 = -b1 + a1 = (-a) + a + b
So it is sufficient to have a group. Can we show anything about what is neccesary to swap any two elements using say only two binary operators?
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