Finally my Ph.D. trip came to its end on Tuesday, September 19, 2017! I successfully defended my thesis in the presence of tens of my friends and professors. Some of them traveled many miles from other cities of the country like Kashan, Arak, Tabriz, Karaj, Zanjan, Kerman and Isfahan to reach Tehran and attend my defense session at Amirkabir University of Technology. Many of them have helped me accomplish my Ph.D. dissertation in one way or another. Thanks to them all for all their kind support during all these years.

Now I am at the end of an old road and beginning of a new journey to a new world of wonders. The original flame of love towards mathematics and fundamental questions of the nature, which I carry in my heart since elementary school era, is still flourishing and motivates me to ask, search and learn more and more. It is a truly unique and wonderful sensation, a kind of re-birth, and I am going to keep it as it is. Hope my humble past and future contributions to mathematical logic, especially set theory, will be useful for the community at least as a source of inspiration for deeper research in the same direction.