An important projective invariant, the cross-ratio of four collinear points, is defined. Some special configurations in two, three and four dimensions are introduced, including extensions of Desargues’ theorem, Sylvester’s ‘duads and synthemes’, desmic systems of tetrahedra, and Baker’s remarkable configuration derived from six points in a complex four-dimensional space.


Projective Transformation Collinear Point Harmonic Conjugate Diagonal Point Reference Triangle 
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Copyright information

© Springer-Verlag London 2013

Authors and Affiliations

  • Eric Lord
    • 1
  1. 1.BangaloreIndia

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