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m 
(Corrected minus sign reflecting Lorentzian signature) 

:<math>ds^2=dt^2+\delta_{ij}dx^i dx^j</math>,
with <math>i,j=1,\dots,d</math> we have
:<math>ds^2=
with <math>i,j=1,\dots,d1</math>, <math>x^+=\frac{t+x}{\sqrt{2}}</math> and <math>x^=\frac{tx}{\sqrt{2}}</math>.

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