
doi: 10.1007/bf01404105
A Herbrand strategy T is that algorithm which for an arbitrary prenex formula F gives a sequence of its Herbrand disjunctions. Let FT be the first tautology in this sequence. T is complete if for every deducible F, FT exists. The strategy T gives k superfluous terms for F if k disjuncts can be removed from FT while preserving its tautological character; T is optimal for F if there exists no Herbrand disjunction for F shorter than FT. There are complete strategies that give arbitrarily small proportion of terms for all F. There are also strategies that work with incomplete information about F (e.g., with the signature of F or a list of its elementary subformulas). For any such complete strategy we can construct a class of formulas for which the proportion of superfluous terms tends to 1 as the length of the formula tends to ∞. However, there is no possible algorithm for finding the superfluous terms which may be dropped. Even for strategies that require complete and uniform review of all possible permutations of terms (for a given signature), the class of formulas for which T is optimal is undecidable. The proof uses properties of the relation “F is more deducible than G,” studied in terms of the general theory of calculi.
Herbrand strategies, stronger deducibility, Classical first-order logic, proof theory, Proof theory and constructive mathematics
Herbrand strategies, stronger deducibility, Classical first-order logic, proof theory, Proof theory and constructive mathematics
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