Let P be a point;  Ha, Hb, Hc the orthocenters of PBC, PCA, PAB. Then concur:
1) The Euler lines of AHbHc, BHcHa, CHaHb
2) The circles {AHbHc}, {BHcHa}, {CHaHb}
3) The ninecircles of AHbHc, BHcHa, CHaHb, HaBC, HbCA, HcAB (only the first three are shown)
4) The circles {HaBC}, {HbCA}, {HcAB}