fCube: An Efficient Prover for Intuitionistic Propositional Logic

In this system description we provide FCUBE, a theorem prover for Intuitionistic propositional logic based on a tableau calculus. The main novelty of cube is that it implements several optimization techniques that allow to prune the search space acting on different aspects of the proof-search. We tested the efficiency of our techniques by comparing FCUBE with other theorem provers. We found that our prover outperforms the other provers on several interesting families of formulas

Tracing orbital images on ultrafast time scales

Frontier orbitals determine fundamental molecular properties such as chemical reactivities. Although electron distributions of occupied orbitals can be imaged in momentum space by photoemission tomography, it has so far been impossible to follow the momentum-space dynamics of a molecular orbital in time, for example, through an excitation or a chemical reaction. Here, we combined time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measured the full momentum-space distribution of transiently excited electrons, connecting their excited-state dynamics to real-space excitation pathways. Because in molecules this distribution is closely linked to orbital shapes, our experiment may, in the future, offer the possibility of observing ultrafast electron motion in time and space