Here we consider the three circles with diameters the segments (X

In the reference, given above, it is proved that there is an involutive homography f on line (e) interchanging the elements of the pairs (X

The fixed points H

The remarks made here can be useful for the determination of the fixed points of the involution (if any). This, for example, can be used to construct the conic passing through four points and tangent to a line, see FourPtsAndTangent.html .

DesarguesInvolution2.html

DesarguesInvolution3.html

DesarguesInvolutionComplex.html

FourPtsAndTangent.html

Involution.html

InvolutionBasic2.html

InvolutionBasic3.html

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