| Links' Seminars and Public Events |   |
| 2023 | |
|---|---|
Fri 20th Jan 11:00 am 12:00 pm | Seminar by Tito Speaker: Lê Thành Dũng Nguyễn, aka “Tito” — nguyentito.eu/ Title: Polyregular functions: some recent developments Abstract: The class of polyregular functions is composed of the string-to-string functions computed by pebble transducers. While this machine model (which extends two-way finite transducers) is two decades old, several alternative characterizations of polyregular functions have been discovered recently [Bojańczyk 2018; Bojańczyk, Kiefer & Lhote 2019], demonstrating their canonicity. The name comes from the polynomial bound on the growth rate of these functions: |f(w)| = |w|^O(1) where |w| is the length of the string w. In this talk, after recalling this context, I will present some subsequent developments in which I have been involved: * the subclass of comparison-free polyregular (or “polyblind”) functions, definable through a natural restriction of pebble transducers, which Pierre Pradic and I actually discovered while studying a linear λ-calculus; * some results that either relate the growth rate of a polyregular function (comparison-free or not) to the “resources” needed to compute it, or show that there is no such relationship. |
Fri 13th Jan 11:00 am 12:00 pm | Seminar by Sarah Winter Speaker: Sarah Winter — sarahwinter.net/ Title: A Regular and Complete Notion of Delay for Streaming String Transducers Abstract: The notion of delay between finite transducers is a core element of numerous fundamental results of transducer theory. The goal of this work is to provide a similar notion for more complex abstract machines: we introduce a new notion of delay tailored to measure the similarity between streaming string transducers (SST). We show that our notion is regular: we design a finite automaton that can check whether the delay between any two SSTs executions is smaller than some given bound. As a consequence, our notion enjoys good decidability properties: in particular, while equivalence between non-deterministic SSTs is undecidable, we show that equivalence up to fixed delay is decidable. Moreover, we show that our notion has good completeness properties: we prove that two SSTs are equivalent if and only if they are equivalent up to some (computable) bounded delay. Together with the regularity of our delay notion, it provides an alternative proof that SSTs equivalence is decidable. Finally, the definition of our delay notion is machine-independent, as it only depends on the origin semantics of SSTs. As a corollary, the completeness result also holds for equivalent machine models such as deterministic two-way transducers, or MSO transducers. This is joint work with Emmanuel Filiot, Ismaël Jecker, and Christof Löding. |
