The author is very grateful to Sergei Kopeikin for useful remarks on this work. It is a pleasure to thank
Silvano Bonazzola, Thibault Damour, Jürgen Ehlers, Gilles Esposito-Farèse, Guillaume Faye, Eric
Gourgoulhon, Bala Iyer, Misao Sasaki, Gerhard Schäfer, Bernd Schmidt, Kip Thorne, and Clifford Will for
interesting discussions and/or collaborations.