Sign Noncontradictory Path ample Given proposition(A→B)→(A→O)→(B→C, there is a truth valuation which make it false Consider the tableau with the root as F(A→B)→(A→C)→(B→OSign & Noncontradictory Path . Example . . Given proposition ((A → B) → (A → C)) → (B → C), there is a truth valuation which make it false. Consider the tableau with the root as F ((A → B) → (A → C)) → (B → C) Yi Li (Fudan University) Discrete Mathematics April 16, 2013 8 / 17