Rule of Specification: Suppose u is a variable which occurs inside the string x. If the string $$\forall u:x$$ is a theorem, then so is x, and so are any strings made from x by replacing u, wherever it occurs, by one and the same term. (Restriction: The term which replaces u must not contain any variable that is quantified in x.)
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#### pdfs

• owner: piotr.wasik - (no access) - Douglas Hofstadter "Goedel, Escher, Bach", p217
• owner: naraypv - (no access) - Gödel, Escher, Bach_ An Eternal Golden Braid-Basic Books (1994).pdf, p225