# Simple QE for Dense Linear Orders

Example of dense linear order: rational numbers with less-than relation. (It works in the same way for real numbers with less-than relation.)

## Theory of Dense Linear Orders

Language . Atomic formulas are of two forms:

• • Literals are either atomic formulas or their negations.

Formulas are the formulas that are closed formulas that are true in the structure or rational numbers.

Example: The 'successor' formula: 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

We have seen that it suffices to eliminate quantifiers from conjunctions of literals.

Can we assume that literals are of a special form?

Example: simplify these formulas:

• • If we have three concrete values for , 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 of axioms, we may be able to show that the atomic type formulas have a simple form

## 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.