5 research outputs found
A Hierarchy of Nondeterminism
We study three levels in a hierarchy of nondeterminism: A nondeterministic
automaton is determinizable by pruning (DBP) if we can obtain a
deterministic automaton equivalent to by removing some of its
transitions. Then, is good-for-games (GFG) if its nondeterministic
choices can be resolved in a way that only depends on the past. Finally, is semantically deterministic (SD) if different nondeterministic choices in
lead to equivalent states. Some applications of automata in formal
methods require deterministic automata, yet in fact can use automata with some
level of nondeterminism. For example, DBP automata are useful in the analysis
of online algorithms, and GFG automata are useful in synthesis and control. For
automata on finite words, the three levels in the hierarchy coincide. We study
the hierarchy for B\"uchi, co-B\"uchi, and weak automata on infinite words. We
show that the hierarchy is strict, study the expressive power of the different
levels in it, as well as the complexity of deciding the membership of a
language in a given level. Finally, we describe a probability-based analysis of
the hierarchy, which relates the level of nondeterminism with the probability
that a random run on a word in the language is accepting.Comment: 21 pages, 5 figure
A Hierarchy of Nondeterminism
We study three levels in a hierarchy of nondeterminism: A nondeterministic
automaton is determinizable by pruning (DBP) if we can obtain a
deterministic automaton equivalent to by removing some of its
transitions. Then, is good-for-games (GFG) if its nondeterministic
choices can be resolved in a way that only depends on the past. Finally, is semantically deterministic (SD) if different nondeterministic choices in
lead to equivalent states. Some applications of automata in formal
methods require deterministic automata, yet in fact can use automata with some
level of nondeterminism. For example, DBP automata are useful in the analysis
of online algorithms, and GFG automata are useful in synthesis and control. For
automata on finite words, the three levels in the hierarchy coincide. We study
the hierarchy for B\"uchi, co-B\"uchi, and weak automata on infinite words. We
show that the hierarchy is strict, study the expressive power of the different
levels in it, as well as the complexity of deciding the membership of a
language in a given level. Finally, we describe a probability-based analysis of
the hierarchy, which relates the level of nondeterminism with the probability
that a random run on a word in the language is accepting.Comment: 21 pages, 5 figure
ICAMs Are Not Obligatory for Functional Immune Synapses between Naive CD4Â T Cells and Lymph Node DCs
Protective immune responses depend on the formation of immune synapses between T cells and antigen-presenting cells (APCs). The two main LFA-1 ligands, ICAM-1 and ICAM-2, are co-expressed on many cell types, including APCs and blood vessels. Although these molecules were suggested to be key players in immune synapses studied in vitro, their contribution to helper T cell priming in vivo is unclear. Here, we used transgenic mice and intravital imaging to examine the role of dendritic cell (DC) ICAM-1 and ICAM-2 in naive CD4 T cell priming and differentiation in skin-draining lymph nodes. Surprisingly, ICAM deficiency on endogenous CD40-stimulated lymph node DCs did not impair their ability to arrest and prime CD4 lymphocyte activation and differentiation into Th1 and Tfh effectors. Thus, functional T cell receptor (TCR)-specific helper T cell synapses with antigen-presenting DCs and subsequent proliferation and early differentiation into T effectors do not require LFA-1-mediated T cell adhesiveness to DC ICAMs