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.