Logic / Logic 269 · Atom · ~20 seconds
Existential Instantiation
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From (∃x)Fx, derive Fa — where a is a name *new to the proof*.
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Something did it; call it a. But a must be a fresh name, carrying no prior commitments.
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The strictest restriction in the system. Reusing an existing name quietly asserts that two somethings are the same something.