 There is another form of independence, strong independence, that even 1-entailment fails to satisfy. If we are given one exception to a rule involving a given antecedent, then we are unable to use any conditional with the same antecedent to derive any conclusion whatsoever. Suppose, for example, that we know that birds fly \((B \Rightarrow F)\), Tweety is a bird that doesn’t fly \((B \amp \neg F)\), and birds lay eggs \((B \Rightarrow E)\). Even under 1-entailment, the conclusion that Tweety lays eggs \((E)\) fails to follow. This failure to satisfy Strong Independence is also known as the Drowning Problem (since all conditionals with the same antecedent are “drowned” by a single exception).