1) The sides of the [diagonal] triangle are divided harmonically by the sides of the quadrangle. For example, in the figure below L, M are harmonic conjugate to G, F.

2) The sides of the complete quadrangle are also divided harmonically by the sides of the [diagonal triangle]. For example, G, I are conjugate to C, A.

3) The intersection points of the sides of the quadrangle and the sides of the [diagonal triangle] are, by three collinear. For example H, L, J are collinear. By the way, the line of H, L, J is the [trilinear polar] of the point A with respect to the triangle EFG.

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