The above solutions were written up in the **Fitch proof editor**.

…

Examples of Fitch Proofs:

1. | Prove q from the premises: p ∨ q, and ¬p. | Solution |
---|---|---|

2. | Prove p ∧ q from the premise ¬(¬p ∨ ¬q) | Solution |

3. | Prove ¬p ∨ ¬q from the premise ¬(p ∧ q) | Solution |

4. | Prove a ∧ d from the premises: a ∨ b, c ∨ d, and ¬b ∧ ¬c | Solution |

## What is a Fitch proof?

Fitch-style proofs **arrange the sequence of sentences that make up the proof into rows**. A unique feature of Fitch notation is that the degree of indentation of each row conveys which assumptions are active for that step.

## How do you make a proof?

**Strategy hints for constructing proofs**

- Be sure that you have translated or copied the problem correctly. …
- Similarly, make sure the argument is valid. …
- Know the rules of inference and replacement intimately. …
- If any of the rules still seem strange (illogical, unwarranted) to you, try to see why they are valid.

## How do you do logic proofs?

Like most proofs, logic proofs usually begin with premises — statements that you’re allowed to assume. The conclusion is the statement that you need to prove. The idea is to operate on the premises using rules of inference until you arrive at the conclusion.

## How do you cite a sentence in Fitch?

**Always cite just two prior lines**. Instructions for use: Introduce a sentence on any line of a proof that changes one or more occurrences of a name from a previous sentence. Cite that sentence you are changing, and cite the identity sentence that says the change you are making is legitimate.

## How do you use disjunction elimination?

An example in English: If I’m inside, I have my wallet on me. If I’m outside, I have my wallet on me. It is true that either I’m inside or I’m outside.

## What is natural deduction in artificial intelligence?

Natural Deduction (ND) is a common name for the class of proof systems composed of simple and self-evident inference rules based upon methods of proof and traditional ways of reasoning that have been applied since antiquity in deductive practice.

## What does a formal proof need to have?

A formal proof of a statement is a sequence of steps that links the hypotheses of the statement to the conclusion of the statement using only **deductive reasoning**. The hypotheses and conclusion are usually stated in general terms.

## What are the three types of proofs?

There are many different ways to go about proving something, we’ll discuss 3 methods: **direct proof, proof by contradiction, proof by induction**. We’ll talk about what each of these proofs are, when and how they’re used.

## What is a good proof?

The fundamental aspects of a good proof are **precision, accuracy, and clarity**. A single word can change the intended meaning of a proof, so it is best to be as precise as possible. There are two different types of proofs: informal and formal.

## When can you close a Subproof?

A subproof is only closed **when the vertical line for that subproof ends**. To put it another way, you can’t end a proof and still have two vertical lines going.

## How do you do conditional elimination?

Quote from the video:

Youtube quote: *You need two formulas one two conditional and the second formula must be the formula that comes to the left of the the arrow.*

## What is disjunctive addition?

Disjunction introduction or addition (also called or introduction) is **a rule of inference of propositional logic and almost every other deduction system**. The rule makes it possible to introduce disjunctions to logical proofs. It is the inference that if P is true, then P or Q must be true.

## Is or disjunctive or conjunctive?

The word “and” is conjunctive, meaning it combines things. Conversely, the word “or” is **disjunctive**, meaning it separates things.

## What is the difference between conjunctive and disjunctive?

As adjectives the difference between disjunctive and conjunctive. is that **disjunctive is not connected; separated while conjunctive is (astrology|astronomy) relating to a conjunction** (appearance in the sky of two astronomical objects with the same right ascension or the same ecliptical longitude).

## What is a positive Subformula?

A positive subformula is **any subformula that is not itself a subformula of a negation, nor a subformula of the antecedent of a conditional**. There are negations on every line of the derivation.