# How does this propositional proof make sense?

Contents

## What is a proof in propositional logic?

In general, to prove a proposition p by contradiction, we assume that p is false, and use the method of direct proof to derive a logically impossible conclusion. Essentially, we prove a statement of the form ¬p ⇒ q, where q is never true. Since q cannot be true, we also cannot have ¬p is true, since ¬p ⇒ q.

## What is an example of a propositional statement?

For example, in terms of propositional logic, the claims, “if the moon is made of cheese then basketballs are round,” and “if spiders have eight legs then Sam walks with a limp” are exactly the same. They are both implications: statements of the form, P→Q. P → Q .

## How do you explain propositional logic?

Propositional logic, also known as sentential logic, is that branch of logic that studies ways of combining or altering statements or propositions to form more complicated statements or propositions. Joining two simpler propositions with the word “and” is one common way of combining statements.

## What does P → Q mean?

p → q (p implies q) (if p then q) is the proposition that is false when p is true and q is false and true otherwise. Equivalent to —not p or q“ Ex. If I am elected then I will lower the taxes.

## How do you prove a theorem in logic?

To prove a theorem you must construct a deduction, with no premises, such that its last line contains the theorem (formula). To get the information needed to deduce a theorem (the sentence letters that appear in the theorem) you can use two rules of sentential deduction: EMI and Addition.

## How do you solve propositional logic?

The first one which we call a says we are both telling the truth and B says a is lying and so we want to do is try to analyze this and figure out who's telling the truth and who's lying.

## What is a propositional logic explain in your own words and give examples to illustrate?

Definition: A proposition is a statement that can be either true or false; it must be one or the other, and it cannot be both. EXAMPLES. The following are propositions: – the reactor is on; – the wing-flaps are up; – John Major is prime minister.

## How do you know if it is a proposition?

This kind of sentences are called propositions. If a proposition is true, then we say it has a truth value of “true”; if a proposition is false, its truth value is “false”. For example, “Grass is green”, and “2 + 5 = 5” are propositions. The first proposition has the truth value of “true” and the second “false”.

## Why do we need to learn about proposition?

The concept of propositions is relevant because it allows us to state or restate claims in an argument to make the argument clearer or to structure the argument so it can be put into logical form as long as the statement we make captures the same exact meaning or propositional content.

## Where is propositional logic used?

It has many practical applications in computer science like design of computing machines, artificial intelligence, definition of data structures for programming languages etc. Propositional Logic is concerned with statements to which the truth values, “true” and “false”, can be assigned.

## Which of the following is a proposition?

A proposition is a declarative sentence that is either true or false (but not both). For instance, the following are propositions: “Paris is in France” (true), “London is in Denmark” (false), “2 < 4” (true), “4 = 7 (false)”.

## How do you prove and statement?

Proving “or” statements: To prove P ⇒ (Q or R), procede by contradiction. Assume P, not Q and not R and derive a contradiction. Proofs of “if and only if”s: To prove P ⇔ Q. Prove both P ⇒ Q and Q ⇒ P.

## How do you make a proof?

Writing a proof consists of a few different steps.

1. Draw the figure that illustrates what is to be proved. …
2. List the given statements, and then list the conclusion to be proved. …
3. Mark the figure according to what you can deduce about it from the information given.

## What is proof writing in math?

A proof is an argument to convince your audience that a mathematical statement is true. It can be a calcu- lation, a verbal argument, or a combination of both. In comparison to computational math problems, proof writing requires greater emphasis on mathematical rigor, organization, and communication.