From Osher Doctorow
If x = z in D1xyz, we get:
1) y(1 + y) + (y - x)(1 - x) -yx - x = 0
which when multiplied out is:
2) y + y^2 + y - yx - x + x^2 - yx - x = 0
or in other words:
3) 2(y - x - yx) = -x^2 - y^2
and since y - x - yx is (y o x)*, we get:
4) 2(y o x)* = - (x^ + y^2)
or in other words:
5) (y o x)* = -(1/2)(x^2 + y^2)
Osher Doctorow
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