From ($x)(y)Fxy we can validly infer ($x)Fxa, assuming that "a" is not found earlier in the proof.

Name: From ($x)(y)Fxy we can validly infer ($x)Fxa, assuming that "a" is not found earlier in the proof.
Brand: Quizplus
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Question

Quizplus · Accepted Answer

The inference is invalid because ($x)(y)Fxy means there exists an x such that for all y, Fxy holds. From this, we cannot infer that there exists an x such that Fxa holds for a specific a, as "a" is not universally quantified.

From ($X)(y)Fxy We Can Validly Infer ($X)Fxa, Assuming That "A