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sav08:simple_qe_for_dense_linear_orders [2009/04/21 19:28] vkuncak |
sav08:simple_qe_for_dense_linear_orders [2009/04/22 00:02] vkuncak |
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Formulas $T$ are the formulas that are closed formulas that are true in the structure $(\mathbb{Q},<)$ or rational numbers. | Formulas $T$ are the formulas that are closed formulas that are true in the structure $(\mathbb{Q},<)$ or rational numbers. | ||
+ | |||
+ | **Example:** The 'successor' formula: | ||
+ | \[ | ||
+ | \forall x. \exists y.\ x < y \ \land\ (\forall z. (x < z \rightarrow z=y \lor y < z) | ||
+ | \] | ||
+ | Is this formula true in dense linear orders? Is there a non-dense linear order where its truth value is different? | ||
===== Normal form of Formulas ===== | ===== Normal form of Formulas ===== | ||
Line 18: | Line 24: | ||
Can we assume that literals are of a special form? | Can we assume that literals are of a special form? | ||
- | **Example:** simplify the formula | + | **Example:** simplify these formulas: |
- | \[ | + | * $x < y\ \land\ \lnot (y < z) \ \land\ (x \neq z)$ |
- | x < y\ \land\ \lnot (y < z) \ \land\ (x \neq z) | + | * $x < y\ \land y < x$ |
- | \] | + | |
+ | If we have three concrete values for $x,y,z$, what is the form of the strongest type of a formula that we could write about them in this language? //(atomic type formula)// | ||
+ | |||
+ | Theorem: every quantifier-free formula in a language with only relational symbols is a disjunction of atomic type formulas | ||
+ | * if we know the set $T$ of axioms, we may be able to show that the atomic type formulas have a simple form | ||
===== Quantifier Elimination Step ===== | ===== Quantifier Elimination Step ===== | ||
+ | Quantifier elimination from atomic type formulas: | ||
+ | |||
+ | Quantifier elimination from more general formulas: | ||
+ | |||
+ | **Example:** Use quantifier elimination to compute the truth value in dense linear orders for the example 'successor' formula above. | ||
+ | |||
+ | ===== References ===== | ||
* [[http://www4.informatik.tu-muenchen.de/~nipkow/pubs/lqe.pdf|Linear Quantifier Elimination]] | * [[http://www4.informatik.tu-muenchen.de/~nipkow/pubs/lqe.pdf|Linear Quantifier Elimination]] |