On September 5, 2025, the teachers of the Department of Higher Mathematics and Statistics took part in the IMPRESS-U seminar on wave equations and quadratic pencils. The report was delivered by Hrehory Berkolayko (Texas A&M University, Texas, USA). The issues of convergence of quantum mechanics operators given on metric graphs when the length of one of the edges of the graph tends to zero were considered. The report caused a lively discussion, in which Professor Pyvovarchyk V.M. and Associate Professor Kalyuzhny-Verbovetsky D.S. participated.