$ x +^{-1} y $ seems like a good notation in that $x^{-1}+^{-1} y^{-1}=(x+y)^{-1} $, and $$ \frac{1}{x}\frac{1}{+}\frac{1}{y} = \frac{1}{x+y} $$ (is this the "Freshman's Dream" in another incarnation?)
Bjørn Kjos-Hanssen
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