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I'm trying to find an on-line source for the "Jacobian Invariant" of four points on a line.

The cross-ratio depends on the order of the points, while this one doesn't.

I've done several Google searches and can't seem to find anything.

Does anyone know of a good source off-hand?

Fly by Night
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1 Answers1

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The commonly used name is $j$-invariant. See here or here (you will have to read a little to realize that they are talking about the same thing!)

Igor Rivin
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