Let Ma, Mb, Mc be the midpoints of the sides. Let Mab, Mac the orthogonal projections of Ma on the pperpendicular bisectors of AB, CA. Define cyclically Mbc, Mba, Mca, Mcb. Let La be the radical axis between {AMbaMca}, {AMabMac} and define cyclically Lb, Lc. The lines La, Lb, Lc concur at the retrocenter R.