The failure to synthesize a compound, to observe a particular property, or to effect a particular reaction can never be positive proof of the nonexistence of that compound, property, or reaction.

• 失败于合成一个化合物,不能观察到特殊性质或者不能影响一个特殊的反应,这些对于判定那个化合物及其性质、反应不存在并非积极证据。