Proof Definition o a tableau proof of a proposition a is a contradictory tableau with root entry Fa. A proposition is tableau provable, written H a, if it has a tableau proof o a tableau refutation for a proposition a is a contradictory tableau starting with Ta. A proposition is tableau refutable if it has a tableau refutationProof . Definition . . 1. A tableau proof of a proposition α is a contradictory tableau with root entry Fα. A proposition is tableau provable, written ⊢ α, if it has a tableau proof. 2. A tableau refutation for a proposition α is a contradictory tableau starting with Tα. A proposition is tableau refutable if it has a tableau refutation. Yi Li (Fudan University) Discrete Mathematics April 9, 2013 8 / 14