Jan Vonk, On the Nagel line and a prolific polar triangle,
Forum Geometricorum, 8 (2008) 183--196.

Abstract: For a given triangle ABC, the polar triangle of the medial triangle with respect to the incircle is shown to have as its vertices the orthocenters of triangles AIB, BIC and AIC. We prove results which relate this polar triangle to the Nagel line and, eventually, to the Feuerbach point.

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