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Published online by Cambridge University Press: 20 January 2009
What is meant will best be understood by the following:-
1. Suppose we have an unlimited straight line XX′ (fig.24) with a finite point O on it. Take two points on the line, C and C1 in the same sense with respect to O such that OC·OC1=a2. Then C and C1 are connected by inversion, and O is the centre inversion. Without loss of generality for what follows we may, for convenience, take a2=12=1, so that OC·OC1=1.