## What does it mean if two formulas are equivalent in first order logic?

**Two first-order formulas F and G over a signature σ are logically equivalent**, denoted F ≡ G, if for all σ-assignments A we have A |= F iff A |= G.

## Is proposition ∀ x P x )) True or false if the domain of X is empty?

true

If the domain is empty, ∀xP(x) is **true** for any propositional function P(x), since there are no counterexamples in the domain. to observe that P(3) is false.

## What is the purpose of the universal and existential quantifiers?

The universal quantifier, meaning “for all”, “for every”, “for each”, etc. The existential quantifier, meaning “for some”, “there exists”, “there is one”, etc. A statement of the form: x, if P(x) then Q(x). A statement of the form: x such that, if P(x) then Q(x).

## How do you prove predicate logic validity?

An argument expressed with sentences in predicate logic is valid **if and only if the conclusion is true in every interpretation in which all the premises are true**.

## What is the truth value of ∃ xP X?

Question: what is the truth value of ∃xP(x)? Question: what is the truth value of ∃xP(x)? Answer: **it is false**. For any real numbers such that b2 < 4ac, there will only be complex solutions, for these cases no such real number x can satisfy the predicate.

## What does ∃ mean in math?

there exists

Page 1. Math 295. Handout on Shorthand The phrases “for all”, “there exists”, and “such that” are used so frequently in mathematics that we have found it useful to adopt the following shorthand. The symbol ∀ means **“for all” or “for any”**. The symbol ∃ means “there exists”.

## Is 0 a real number?

**Real numbers can be positive or negative, and include the number zero**. They are called real numbers because they are not imaginary, which is a different system of numbers. Imaginary numbers are numbers that cannot be quantified, like the square root of -1.

## What do curly braces mean in math?

Braces or curly brackets { } are **used when the domain or range consists of discrete numbers and not an interval of values**. If the domain or range of a function is all numbers, the notation includes negative and positive infinity (−∞,∞). If the domain is all positive numbers plus 0, the domain would be written as [0,∞).

## What does U and upside down U mean?

What is U and upside down U in math? In math, the symbol **U represents the union of two sets, while upside-down U represents the intersection of the sets**.

## What does ∩ mean in math?

intersection

∩ The symbol ∩ means **intersection**. Given two sets S and T, S ∩ T is used to denote the set {x|x ∈ S and x ∈ T}. For example {1,2,3}∩{3,4,5} = {3}. \ The symbol \ means remove from a set. Given two sets S and T, S\T is used to denote the set {x|x ∈ S and x /∈ T}.

## What is reverse U in math?

**“Intersect”** is represented by an upside down U. The intersection is where the circles overlap. “Union” is represented by a right-side up U. The union is the entire area of both circles.