In India the word “GURU” is a revered one. A Guru is not a person from whom you just learn something but someone who changes your view of the world. Jon changed my view of mathematics. I had been studying papers by Jon since my Phd days but first met him 2009 in Adelaide in the AustMS conference. He immediately invited me to visit him in Newcastle which I did and spent three lovely days there and enjoyed the warm the hospitality of Jon and Judi. Further it was unnerving for me to see Jon handle so many different areas in mathematics in such a natural fashion. It was an awe-inspiring experience. Jon understood my nervousness and made me very comfortable and gave me the permission to ask him any mathematical question I like even when I am back in India. In fact from 2009 to 2016 whenever I had faced a very difficult issue in convex analysis or optimization which I failed to resolve or understand I used to write an email to Jon for help and surely within a few minutes I got the answer and with a couple more papers on the particular issue attached. Such was his generosity. In 2013, Jon visited India to deliver talks in CIMPA school and I spent a few more lovely days travelling around Delhi with him and Judi. In fact during a dinner in a restaurant in Delhi, Jon asked me to be a co-author with him on a problem book on convex and nonsmooth analysis. I was completely taken aback that such a great mathematician considered me to be his co-author. This was a great honour for me. I visited Jon in Newcastle for a month and ten days in 2014. This was one of the most exciting periods in my career. I learned so much from Jon even when we just walked together to the cafe for lunch. During these walks I not only learned new things about optimization but also about mathematics itself and he changed my view of mathematics and I can now read books in some other areas of mathematics which I would otherwise never take a look at. Jon and Judi were excellent hosts and took me to lovely places in Australia including a fabulous trip to do whale watching. Even during this trips he spoke to me about mathematics but also about history and economics. His breadth of knowledge was so much that I was in fact learning things in other fields too. During one of my talks on gap functions for variational inequalities and CARMA Jon immediately connected it to Fitzpatrick function and that lead to joint paper which is now online. It was such a joy to be his co-author he was very demanding but the end result was so nice. To be his co-author is one of the highest point of my career. I am so shocked that he just passed away when the problem book writing gained momentum and we started talking on another joint work. Jon was my mathematical guru in true sense of the word. May his soul rest in peace while I would like devote myself to the view of mathematics that he had shown me. [Joydeep Dutta, Indian Institute of Technology, Kanpur, India]