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- Yijia Chen, Martin Grohe, Magdalena Grüber
- Electronic Colloquium on Computational Complexity
- 2006

Combining classical approximability questions with parameterized complexity, we introduce a theory of parameterized approximability. The main intention of this theory is to deal with the efficient… (More)

- Yijia Chen, Jörg Flum
- CSL
- 2003

We give machine characterizations of the complexity classes of the W-hierarchy. Moreover, for every class of this hierarchy, we present a parameterized halting problem complete for this class.

- Yijia Chen, Jörg Flum, Martin Grohe
- 18th IEEE Annual Conference on Computational…
- 2003

We give machine characterisations and logical descriptions of a number of parameterized complexity classes. The focus of our attention is the class W[P], which we characterise as the class of all… (More)

- Yijia Chen, Marc Thurley, Mark Weyer
- ICALP
- 2008

We study left-hand side restrictions of the induced subgraph isomorphismproblem: Fixing a class , for given graphs G and arbitrary Hwe ask for induced subgraphs of Hisomorphic to G.
For the… (More)

- Yijia Chen, Jörg Flum, Moritz Müller
- Theory of Computing Systems
- 2010

We first present a method to rule out the existence of parameter non-increasing polynomial kernelizations of parameterized problems under the hypothesis P≠NP. This method is applicable, for example,… (More)

- Yijia Chen, Jörg Flum, Martin Grohe
- Theor. Comput. Sci.
- 2005

We give machine characterizations of most parameterized complexity classes, in particular, of W[P], of the classes of the W-hierarchy, and of the A-hierarchy. For example, we characterize W[P] as the… (More)

- Yijia Chen, Jörg Flum
- Twenty-Second Annual IEEE Conference on…
- 2007

We study the parameterized complexity of various path (and cycle) problems, the parameter being the length of the path. For example, we show that the problem of the existence of a maximal path of… (More)

- Yijia Chen, Jörg Flum
- Fields of Logic and Computation
- 2010

- Yijia Chen, Jörg Flum
- J. Symb. Log.
- 2010

The undecidability of first-order logic implies that there is no computable bound on the length of shortest proofs of valid sentences of first-order logic. Some valid sentences can only have quite… (More)

- Yijia Chen, Jörg Flum
- J. ACM
- 2012

Let C denote one of the complexity classes “polynomial time,” “logspace,” or “nondeterministic logspace.” We introduce a logic <i>L</i>(C)<sub>inv</sub> and show generalizations and variants of the… (More)