I have many things to remember about my friend and guru Rene DAVID. I learnt a lot about Petri nets and Grafcet from him. My PhD work used Petri nets. 
I also managed to get him to India, Hyderabad, to deliver a one-week course on Petri Nets and Grafcet (along with Hassane Alla), in Dec. 1991. This course was conducted on behalf of IEEE Hyderabad, and was sponsored by the French Embassy in India.
He also gifted me 
his book on this subject (which was originaly written in French. I helped him in its translation to English). I cherish this book, till today.
He visited my home, celebrated Christmas with us, inspected and approved the accessible house I had built with the inspiration he had given me in Grenoble, France. It was a memorable experience for my children and me.
Rene might have left us, but his books and his memories will always be with us.
See also : Rene DAVID (RIP)