The Theory Group at KTH Royal Institute of Technology invites applications for a PhD position in theoretical computer science. KTH Royal Institute of Technology is the leading technical university in Sweden. The Theory Group at KTH (http://www.csc.kth.se/tcs/) offers a strong research environment covering a wide range of research topics such as complexity theory and approximation algorithms, computer and network security, cryptography, formal methods and natural language processing. The group has a consistent track record of publishing in the leading theoretical computer science conferences and journals worldwide, and the research conducted here has attracted numerous international awards and grants in recent years. We are now set to expand further, and this position is just one of several new openings. Proving formulas in propositional logic is a problem of immense importance both theoretically and practically. This computational task is widely believed to be intractable in the worst case, although proving (or disproving) this is a major open problem in theoretical computer science and mathematics. (This is one of the famous million dollar Millennium Problems, known as the P vs. NP problem.) In spite of this, today so-called SAT solvers are routinely used to solve large-scale real-world problem instances with millions of variables. The intriguing question of when SAT solvers perform well or badly, and what properties of the formulas explain this behaviour, remains quite poorly understood. Proof complexity studies formal systems for reasoning about logic formulas. This field has deep connections to fundamental questions in computational complexity, but another important motivation is the connection to SAT solving. All SAT solvers use some kind of method or system in which proofs are searched for, and proof complexity analyses the potential and limitations of such proof systems (and thereby of the algorithms using them). Our research aims to advance the frontiers of proof complexity, and to leverage this research to shed light on questions related to SAT solving. We want to understand what makes formulas hard or easy in practice, and to gain theoretical insights into other crucial but poorly understood issues in SAT solving. We are also interested in exploring the possibility of basing SAT solvers on stronger proof systems than are currently being used. In order to do so, however, a crucial step is to obtain a better understanding of the corresponding proof systems, and in this context there are a number of well-known and relatively longstanding open questions in proof complexity that we want to study and try to resolve. This research project is led by Jakob Nordstrom (http://www.csc.kth.se/~jakobn) and is financed by a Breakthrough Research Grant from the Swedish Research Council and a Starting Independent Researcher Grant from the European Research Council. The group currently consists of one postdoctoral researcher and two PhD students (in addition to the project leader). Travel funding is included, and the group also receives short-term and long-term visitors on a regular basis. This is a four-year full-time employed position, but PhD positions usually (but not necessarily) include 20% teaching, in which case they are prolonged for one more year. The successful candidate is expected to start in August-September 2014, although this is to some extent negotiable. The application deadline is December 15, 2013. See http://www.csc.kth.se/~jakobn/openings/D-2013-0620-Eng.php for the full, formal announcement with more information and instructions for how to apply. Informal enquiries about this position are welcome and may be sent to Jakob Nordstrom.