Monadic second-order logic with cardinality predicates ★★

Author(s): Courcelle

The problem concerns the extension of Monadic Second Order Logic (over a binary relation representing the edge relation) with the following atomic formulas:

    \item $ \text{``}\,\mathrm{Card}(X) = \mathrm{Card}(Y)\,\text{''} $ \item $ \text{``}\,\mathrm{Card}(X) \text{ belongs to } A\,\text{''} $

where $ A $ is a fixed recursive set of integers.

Let us fix $ k $ and a closed formula $ F $ in this language.

Conjecture   Is it true that the validity of $ F $ for a graph $ G $ of tree-width at most $ k $ can be tested in polynomial time in the size of $ G $?

Keywords: bounded tree width; cardinality predicates; FMT03-Bedlewo; MSO

Order-invariant queries ★★

Author(s): Segoufin

    \item Does $ {<}\text{-invariant\:FO} = \text{FO} $ hold over graphs of bounded tree-width? \item Is $ {<}\text{-invariant\:FO} $ included in $ \text{MSO} $ over graphs? \item Does $ {<}\text{-invariant\:FO} $ have a 0-1 law? \item Are properties of $ {<}\text{-invariant\:FO} $ Hanf-local? \item Is there a logic (with an effective syntax) that captures $ {<}\text{-invariant\:FO} $?

Keywords: Effective syntax; FMT12-LesHouches; Locality; MSO; Order invariance

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