Following is my SHORTENED letter (2.2006) in honor of Professor Cooperstock's retirement.
A list of his scientific books see at
http://www.netsivi.org/IARDgone.htm

Dear Professor Cooperstock,
We met in the scientific meetings of IARD2000 (Israel), Rome MG9 (2000) and IARD2004. Especially I remember your friendly warm anxiety. In the IARD2004 meeting, the sitting chairs were very hard, and I was surprised when I got very paining cramps in my foot. I told it to you. You already had brought another, a comfortable, soft armchair from a neighboring room, but hearing about my pain, you gave me the armchair to sit on and brought another chair for yourself.

Recent years brought surprising advances in galaxies' research *. Some years ago Doppler measurements of some spiral galaxies showed that the tangential velocities are not Keplerian. Later it was found that this property exists in ALL spiral galaxies. Some explanations were suggested, including changing the Newtonian gravity law, and a huge halo of the dark matter surrounding each spiral galaxy. Last year you, Prof. Cooperstock addressed the problem from a different point of view. Digging deeper into galactic relativistic dynamics, you and your student were able to show that when solving NON-LINEAR RELATIVISTIC equations of the motion of stars in flat galaxies, the tangential velocities result just fitting to the observations, without any need for a new gravity law, or for a huge dark matter halo surrounding each galaxy.

I hope that you will continue to surprise us with new research results. Wishing you a fruitful period of further successful activities,
Yours,
Netsivi Ben-Amots



Comments:
* The original letter was much longer and included a few more discoveries from that time about galaxies, not related to Professor Cooperstock.
Professor Fred Cooperstock passed away January 2018. Let his memory be blessed. Yehi zichro baruch.