منابع مشابه
Tree Canonization and Transitive Closure
We prove that tree isomorphism is not expressible in the language FO TC COUNT This is surprising since in the presence of ordering the language captures NL whereas tree isomorphism and canonization are in L Lin Our proof uses an Ehrenfeucht Fra ss e game for transitive closure logic with counting Gr a IL As a corresponding upper bound we show that tree canonization is expressible in FO COUNT lo...
متن کاملCompressed Tree Canonization
Straight-line (linear) context-free tree (SLT) grammars have been used to compactly represent ordered trees. Equivalence of SLT grammars is decidable in polynomial time. Here we extend this result and show that isomorphism of unordered trees given as SLT grammars is decidable in polynomial time. The result generalizes to isomorphism of unrooted trees and bisimulation equivalence. For non-linear...
متن کاملNested Pebbles and Transitive Closure
First-order logic with k-ary deterministic transitive closure has the same power as two-way k-head deterministic automata that use a finite set of nested pebbles. This result is valid for strings, ranked trees, and in general for families of graphs having a fixed automaton that can be used to traverse the nodes of each of the graphs in the family. Other examples of such families are grids, toru...
متن کاملHybrid Transitive Closure Algorithms
We present a new family of hybrid transitive closure algorithms, and present experimental results showing that these algorithms perform better than existing transitive closure algorithms, includmg matrix-based algorithms that divide a matrix into stripes or into square blocks, and graph-based algmtihms. This family of algorithms can be generalized to solve path problems and to solve problems in...
متن کاملTransitive-closure spanners
We define the notion of a transitive-closure spanner of a directed graph. Given a directed graph G = (V,E) and an integer k ≥ 1, a k-transitive-closure-spanner (k-TC-spanner) of G is a directed graph H = (V,EH) that has (1) the same transitive-closure as G and (2) diameter at most k. These spanners were studied implicitly in access control, property testing, and data structures, and properties ...
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ژورنال
عنوان ژورنال: Information and Computation
سال: 2000
ISSN: 0890-5401
DOI: 10.1006/inco.1999.2835