I was fortunate to be granted sabbatical leave for the 2018-19 academic year, a blessed opportunity to catch up on research and writing after my three-year term as department chair. As I suspected I will not be taking another sabbatical before retirement, I rolled the dice and applied for a Fulbright Award,in particular a Global Scholar award, which allows you to vist up to three countries for at least three months each, in at least two dofferent hemispheres. A bit surprisingly, it was successful. Under that grant I visited Geoff Whittle and Dillon Mayhew and Victoria University of Wellington in Wellington, New Zealand, for ten weeks in early 2019 (summer into autumn), and then, after returning to Flagstaff (on the spring equinox) for two weeks, I visited Clément Dupont and Thomas Haettel at L'Institut Montpellieraine Alexandre Grothendieck (IMAG) at Université de Montpellier, Montpellier, France (between Toulouse and Marseille on the Mediterranean), for a little over ten weeks in the second quarter of 2019 (spring into summer), returning home on the summer solstice. While in Montpellier I took a week to visit Paolo Bellingeri and John Guaschi at the Université de Normandie-Caen in Normandy and spent three days with Henry Crapo in La Vacquerie (near to Montpellier in the countryside).

In the Fall, I had invitations to lecture for a week in a summer school for graduate students and post-docs, organized by graduate students, at Ruhr-Universität Bochum (RUB) in Bochum, Germany, and at a matroid theory conference at Centre International Recherche Mathématiques (CIRM) in Marseille, France, two weeks apart, in September. I parlayed those invitations and a generous research award from my department into a 6-week, 6-city tour visiting colleagues: Dublin, Bochum, Bremen, Marseille, Fribourg, and Dublin again - see below for details.

It was a very successful year: I made substantial progress, both positive and negative, on many projects, and learned a lot from my various hosts, and finished several complicated papers. And I got to see some new parts of the world, meet many interesting people, and have many unique and interesting experiences, mathematical, musical, social, and educational. And, I'm really happy to be back home in Flagstaff, and excited to get back to teaching ...

Here is a listing of the major events, mathematical, musical, and otherwise, during the year. It's unfinished, but I figured I'd post what I've done so far, and continue editing as I have time.

August 27, 2018	My wife Darcy and I set off by car for Madison, Wisconsin, for a family wedding over the Labor Day weekend, driving two-lane highways most of the way. We spent the first night camping at Black Canyon of the Gunnison National Park in Colorado, the next night in a cheap motel in Garden City, Kansas, the next night at her sister's house in Valparaison, Indiana, followed by awedding weekend in Madison, where I lived for six years around 1980, and where we lived during my 1994-95 sabbatical. We stayed at the Concourse - I have no recollection.
September 3 - 9	I flew from Madison to Chicago to Dublin on Labor Day, while Darcy drove home solo. I spent the next week in Dublin talking mathematics with my collaborator/coauthor Tom Brady, of Dublin CIty University. (He played Gaelic football as a youth., never been on the Patriots.) Tom and his mate Colum Watt (from TU Dublin) and I wrote a paper together after my four-month stay there in 2012, that just appeared. (It does take that long sometimes.) On this visit Tom and I made some headway on a couple of ideas, to use this complex we constructed to prove homological stability and/or representation stability of the Milnor fibers of real reflection arrangements and/or finite-type Artin groups. At least now we have something to do, and I have an excuse to go back to visit him. I also had the opportunity to spend two Saturday afternoons at the Cobblestone old-time music sessiion - although it was a bit of a challenge with the mandola I was travelling with (long story). The crowd seemed to like it just fine. On the second Saturday, I remembered on the way home that I used to stop in at the Michael Hughes pub on the way home, where there's an American folk-ish music session, so I stopped in, and, amazing to me, they remembered me. Had a blast - even played an Irish tune for them, since that's all I could think of on a CGAG mandola, and they tolerated it nicely. Turned the wrong way on the way home and go to see the Guinness Storehouse, which I never went to, well after closing time. I stayed in a drafty AirBnB on Drumcondra Road near Home Farm Rd., in my old neightborhood, where I always stay - expense covered by part of an L.M. Perko Faculty Research Grant I received from the NAU math department.
September 9 - 15	I flew from Dublin to Düsseldorf, to then train to Bochum, to give three lectures as part of a summer school on arrangements, organized by graduate students of Gerhard Rohrle. I failed to change trains in Duisburg and ended up waiting on a lonely platform along the Dutch frontier (Empel-Rees, on a major smuggling route, according to Eva and Dima) for the train going back the other way - picked mandola for bit in the night. Met a nice American couple on the train back, an aspiring mando player and an academic. Once I got there, the meeting was a very nice - I got to spend time with my coauthors Graham Denham - we talked about "cographic arrangements" - and Emanuele Delucchi, and Gerhard's student Tilman Möller, and it was nice to be able to hear all the other lecturers. Here is the web page: New Perspectives in Hyperplane Arrangements. We stayed at the Acora Hotel downtown - very nice.I didn't get lost, much.
September 15 - 23	I left Bochum by train for Bremen, where I spent nine very pleasant, quiet days working at Universität Bremen and talking with my colleagues Eva Feichtner and Dmitry Kozlov. The Perko grant covered my meal expenses, and Eva's grant covered a wonderful studio apartment at 7Things - very pleasant all around. Eva and I made some small step forward in our attempt to understand the tropical geometry underlying resonance in Orlik-Solomon algebras. Something else to work on ...
September 23 - 30	I flew from Bremen to Marseille, France, for the conference Combinatorial Geometries 2018: matroids, oriented matroids, and applications, at Centre International de Recherches Mathematiques (CIRM) at the University of Aix-Marseille - here's the web page: CG18-CIRM. I gave a slide talk on work with Delucchi, and with Dana Ernst and Sonja Riedel: Pairs of topes. It was very useful to hesr about current research in matroid theory - I learned a lot. I was able to talk with coauthors Joseph Kung and Delucchi, and got to meet Jo Ellis-Monaghan, one of the editors of the Tutte book that Joseph and I are contributing to, and also is one of the few mathematician alumni of Bennington College, besides me - we may be the only two. It was great to talk about our beloved teachers and otherwise hear more about Bennington - she lives and teaches in Vermiont and so has maintained more contact.It was really good to reconnect with the matroid theory community, many of whom I know from conferences in the 1990's and haven't seen since then. It was great, kinda hot, the food was great. I didn't get lost, much.
September 30 - October 6	I then traveled with Emanuele Delucchi back to his home in Fribourg, Switzerland, for a week-long stay and to give a talk in his department. I gave a general-audience talk about arrangement groups, centered around about my work on Brunnian-like elements with Dan Cohen and Dick Randell. Emanuele and I came up with some new applications of our tope-pair poset Q ("AppliQations"): at long last a complete proof that the cohomology algebra of the Salvetti complex of an oriented matroid is the OS algebra of the underlying matroid (credited to Gelfand and Rybnikov, who gave no proof). The complex |Q| is amenable to deletion/contraction arguments, where the Salvetti complex is completely not so, which allows the proof. I stayed at the Hotel Alpha. I was a little preoccupied by the Kavanagh hearings - my evening soap. Grrr. I did a lot of walking, got lost constantly. Darcy called me the night before I left to tell me the sewer line had failed.
October 6 - 7	I took the train to Zurich and then flew back to Dublin, to get my return flight home, arriving in time for the Saturday afternoon Cobblestone old-time session, according to plan, this time playing a mandolin borrowed from the fiddler Colm, much better. In August, after I had bought all my tickets, I looked at Lisa Hannigan's tour schedule, as I usually do, and discovered she had two nights at the National Concert Hall in Dublin, performing with a contemporary chamber orchestra, Stargaze. I bought a ticket (sixth row, center) for Sunday night, for a magical performance which became her latest album, filmed for several youtube videos - here's what it was like (this opened the show): We The Drowned. I stayed at a different AirBnB in my old neighborhood, this one perfectly located just off Mobhi Road in Glasnevin, walking distance to the Cobblestone. Had a nice chat or two with the permanent tenant there, Margaret, who was "made redundant" in the 2008 crash, took early retirement, and moved from Mayo (or Sligo, can't remember) to Dublin to volunteer as a hospice worker. Boils her chicken, carrots, and potatoes most every night for dinner, eats her fruit first ... I'd stay there again.
October 8 - January 10	The next morning I flew home, to, firstly, watch them excavate our front yard and replace the sewer line, well, firstly to reconnect with my wife, and secondly the sewer line. I spent the next month adding matrerial and revising the OS algebra material in the Falk-Kung book chapter, which the editors were anxious to have - it turned out really nice and will form the basis of the graduate topics course I will teach in Spring, 2020.
January 11 - June 21	This is the period of my Fulbright Global Scholar Award. I spent ten weeks in Wellington, New Zealand, and 10.5 weeks in Montpellier, France, the latter period including side trips to Caen, Normandy, to London, Ontario, and to Henry Crapo's place (Moutons Matheux) in La Vacquerie. I will report on my activities during that time period on a separate page, to be shared with a wider audience, as is my charge as a Fulbrighter. Click here.

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Last updated September 5, 2019

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