Dear Ronnie, I am one of many who will always remember your mathematics, your kindness, and your friendship, and who will greatly miss you. Among other things, you created a new mathematics between category theory and topology, with groupoids and higher groupoids playing a special role in it, which is certainly appreciated but not yet fully understood… I remember, you have kindly sent me one of your Bangor preprints, after which I called you (which was the first telephone call abroad in my life) and we agreed to meet on a Topology Conference in Baku in 1987, and that you will visit Tbilisi after that. Your visit has opened many good doors… I remember Category Theory Conference in Bangor in 1989, whose Proceedings were published in 1991 as three issues of Volume 32 of “Cahiers” together with the Proceedings of its ‘second part’ in Cambridge. In the introduction of that volume, you wrote: “The pair of meetings had a high international participation, notable for the presence of nine colleagues from Tbilisi, two from Moscow and five from Eastern Europe…”. My paper submitted there was called “What is a double central extension? – The question was given by Ronnie Brown”, which you suggested to rename as “What is a double central extension? (the question was asked by Ronald Brown)”, which I did. I remember all your kind invitations to Bangor, and I am very glad we published four joint papers, in JPAA in 1997 and 1999, in APCS in 2004, and, together with George Peschke, in TAC in 2021. I am very glad Maria Manuel Clementino, Marino Gran, Timothy Porter and I edited a special volume of JHRS dedicated to you for your 80th birthday. And let me add here, I am sure you are very proud of you son Marcus, who took such an admirable care of you in your last years in this world. George Janelidze Professor of Mathematics University of Cape Town and Georgian National Academy of Sciences

I first met Ronnie at the University of Hull in 1963 when he supervised my Master's Thesis. I got my Ph.D by published work in 1972 and was in frequent contact with him after that. He was always interested in whatever topics I was working on and always encouraging. In the 1990's and 2000's, I spent multiple summers at the University of Bangor,working on my own research and exchanging ideas with Ronnie and Tim Porter. Ronnie was always welcoming and hospitable. I have to be grateful for that. This was a particularly pleasant time for my wife Nita and myself, as it gave us the opportunity to get to know Snowdonia very well. I count myself lucky to have always had his support in multiple ways. Peter Booth Professor Emeritus Memorial University of Newfoundland Canada

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