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Seminars "Proof Theory" and "Logic Online Seminar"
March 24, 2025 16:00, Moscow, Steklov Mathematical Institute (8 Gubkina), room 313 + online


Ordinal invariants of homomorphic quasiorders of k-labelled forests

V. L. Selivanov, I. V. Smirnov

Saint Petersburg State University

Abstract: The talk discusses the combinatorial complexity of well-partial orders (WPO). WPO theory has a rich history and applications in various areas of mathematics and computer science. The tools of WPO theory include the so-called ordinal invariants, i.e. ordinals measuring certain aspects of the combinatorial complexity of a WPO. Calculating ordinal invariants of specific WPOs (height, width, and maximal ordinal) is often a non-trivial problem, which has been solved to date only for a small number of important WPOs.
In this paper, we calculate (in terms of Veblen ordinals) ordinal invariants for specific WPOs described in the title, they have been introduced by P. Hertling and have found applications in descriptive set theory and automata theory on infinite words.


© Steklov Math. Inst. of RAS, 2025