A Lagrangian fibration
See, for instance, pages 7 and 12 of my article, where this arises in the context of representation theory of SL(2, R).
Announcement: The 2019 Union College Math Conference Friday Sept 13 – Sunday Sept 15.I am co-organizing the session on Differential Geometry, Geometric Analysis, and Mathematical Physics with my colleagues Charles Boyer, Jeff Jauregui, and Christina Tønnesen-Friedman. There will also be parallel sessions in: Applied Topology; History of Mathematics; and Number Theory.Plenary speakers:Robert Ghrist (University of Pennsylvania)Carolyn Gordon (Dartmouth College)Álvaro Lozano-Robledo (University of Connecticut)John McCleary (Vassar College)The website for the conference can be found here.
Ehssan Khanmohammadi
Visiting Assistant Professor of Mathematics
Department of Mathematics
Union College
Schenectady, NY 12308
Office: 108B Bailey Hall
Email: khanmohe@union.edu