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Logical truth is one of the most fundamental concepts in logic.Broadly speaking, a logical truth is a statement which is true regardless of the truth or falsity of its constituent propositions.
Conjectural history is a type of historiography isolated in the 1790s by Dugald Stewart, who termed it "theoretical or conjectural history," as prevalent in the historians and early social scientists of the Scottish Enlightenment. As Stewart saw it, such history makes space for speculation about causes of events, by postulating natural causes ...
Manin–Mumford conjecture; Marden tameness conjecture; Mariño–Vafa conjecture; Milin conjecture; Milnor conjecture (K-theory) Milnor conjecture (knot theory) Modularity theorem; Mordell conjecture; Mordell–Lang conjecture; Mordell's conjecture; Morita conjectures
The converse may or may not be true, and even if true, the proof may be difficult. For example, the four-vertex theorem was proved in 1912, but its converse was proved only in 1997. [3] In practice, when determining the converse of a mathematical theorem, aspects of the antecedent may be taken as establishing context.
No free lunch in search and optimization (computational complexity theory) No free lunch theorem (philosophy of mathematics) No-hair theorem ; No-trade theorem ; No wandering domain theorem (ergodic theory) Noether's theorem (Lie groups, calculus of variations, differential invariants, physics) Noether's second theorem (calculus of variations ...
The compactness theorem first appeared as a lemma in Gödel's proof of the completeness theorem, and it took many years before logicians grasped its significance and began to apply it routinely. It says that a set of sentences has a model if and only if every finite subset has a model, or in other words that an inconsistent set of formulas must ...
The theorem is a syntactic consequence of all the well-formed formulas preceding it in the proof. For a well-formed formula to qualify as part of a proof, it must be the result of applying a rule of the deductive apparatus (of some formal system) to the previous well-formed formulas in the proof sequence.
For example, considering the proposition "all bachelors are unmarried:" its negation (i.e. the proposition that some bachelors are married) is incoherent due to the concept of being unmarried (or the meaning of the word "unmarried") being tied to part of the concept of being a bachelor (or part of the definition of the word "bachelor").