deletions | additions       diff --git a/Gaussian Coordinates.tex b/Gaussian Coordinates.tex  index 779cdee..5501fac 100644  --- a/Gaussian Coordinates.tex  +++ b/Gaussian Coordinates.tex 
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P': (u + du, v + dv),  $$  where $du$ and $dv$ signify very small numbers. In a similar manner we may indicate the distance (line-interval) between $P$ and $P'$, as measured with a little rod, by means of the very small number ds. Then according to Gauss we have   $$   ds^2 = g_{11} du^2 +2g_{12}\,du \,dv + g_{22} dv^2   $$