Christopher J. Bradley, David Monk, and Geoff  C. Smith, On a porism associated with the Euler and Droz-Farny lines,
Forum Geometricorum, 7 (2007) 11--17.

Abstract:  The envelope of the Droz-Farny lines of a triangle is determined to be the inconic with foci at the circumcenter and orthocenter by using purely Euclidean means. The poristic triangles sharing this inconic and circumcircle have a common circumcenter, centroid and orthocenter.

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