fCube: an efficient prover for intuitionistic propositional logic. We present fCube, a theorem prover for intuitionistic propositional logic based on a tableau calculus. The main novelty of fCube is that it implements several optimization techniques that allow to prune the search space acting on different aspects of 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.