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- Pierre Fraigniaud, Ivan Rapaport, Ville Salo, Ioan Todinca
- DISC
- 2016

We study property testing in the context of distributed computing, under the classical CONGEST model. It is known that testing whether a graph is triangle-free can be done in a constant number of rounds, where the constant depends on how far the input graph is from being triangle-free. We show that, for every connected 4-node graph H, testing whether a… (More)

- Jarkko Kari, Martín Matamala, Ivan Rapaport, Ville Salo
- SIROCCO
- 2015

We study the message size complexity of recognizing, under the broadcast congested clique model, whether a fixed graph H appears in a given graph G as a minor, as a subgraph or as an induced subgraph. The n nodes of the input graph G are the players, and each player only knows the identities of its immediate neighbors. We are mostly interested in the… (More)

- Ville Salo, Ilkka Törmä
- MFCS
- 2012

- Jarkko Kari, Ville Salo
- Algebraic Foundations in Computer Science
- 2011

Picture walking automata were introduced by M. Blum and C. Hewitt in 1967 as a generalization of one-dimensional two-way finite automata to recognize pictures, or two-dimensional words. Several variants have been investigated since then, including deterministic, non-deterministic and alternating transition rules; four-, three-and two-way movements;… (More)

- Ville Salo, Ilkka Törmä
- Fundam. Inform.
- 2013

We present constructions of countable two-dimensional subshifts of finite type (SFTs) with interesting properties. Our main focus is on properties of the topological derivatives and sub-pattern posets of these objects. We present a countable SFT whose iterated derivatives are maximally complex from the computational point of view, constructions of countable… (More)

- Ville Salo
- AUTOMATA & JAC
- 2012

We prove a conjecture from [Guillon-Richard '08] by showing that cellular automata that eventually fix all cells to a fixed symbol 0 are nilpotent on S Z d for all d. We also briefly discuss nilpotency on other subshifts, and show that weak nilpotency implies nilpotency in all subshifts and all dimensions, since we do not know a published reference for this.

- Ville Salo, Ilkka Törmä
- Automata
- 2013

- Ville Salo, Ilkka Törmä
- AUTOMATA & JAC
- 2012

We study the computational and structural aspects of countable two-dimensional SFTs and other subshifts. Our main focus is on the topological derivatives and subpattern posets of these objects, and our main results are constructions of two-dimensional countable subshifts with interesting properties. We present an SFT whose iterated derivatives are maximally… (More)

- Ville Salo, Ilkka Törmä
- ArXiv
- 2013

In this article, we prove that for all pairs of primitive Pisot or uniform substitutions with the same dominating eigenvalue, there exists a finite set of block maps such that every block map between the corresponding subshifts is an element of this set, up to a shift. This result is proved using a common generalization of block maps and substitutions,… (More)

- Ville Salo, Ilkka Törmä
- Automata
- 2014

In this article, we study countable sofic shifts of Cantor-Bendixson rank at most 2. We prove that their conjugacy problem is complete for GI, the complexity class of graph isomorphism, and that the existence problems of block maps, factor maps and embeddings are NP-complete.