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Every elliptical involution has the property that there are two definite points in the plane from which any two conjugate points are seen under a right angle.

Circular Involution

Every elliptical involution has the property that there are two definite points in the plane from which…

The lines which join corresponding points in an involution on a conic all pass through a fixed point; and reciprocally, the points of intersection of conjugate lines in an involution among tangents to a conic lie on a line.

Conic Involution

The lines which join corresponding points in an involution on a conic all pass through a fixed point;…

The three points in which any line cuts the sides of a triangle and the projections, from any point in the plane, of the vertices of the triangle on to the same line are six points in involution.

Involution

The three points in which any line cuts the sides of a triangle and the projections, from any point…