All Questions
Tagged with symbolic-logic proof
43
questions
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2
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81
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How is this logic valid?
An excerpt from Logic 2010:
In particular, what is confusing is that it permits assuming the conditional but then reaching a contradiction to prove the conditional. In my experience, that is not a ...
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0
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83
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Need help with this Symbolic Logic Proof please
I am having trouble solving this proof. Line 5 is wrong, I know it's Demorgan's Law, but the proof machine doesn't accept that as an answer. I think it only accepts ~Elim, vElim, vIntro, ~Intro, &...
1
vote
0
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130
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Nested Quantifiers Proof - Logic
When I prove this: -∃x.P(x) ⊢ ∀x.-P(x) [True]
I did it like that:
∀x.-P(x) ⊢ ∀x.-P(x) because (negative ∃) -∃x.P(x) becomes ∀x.-P(x) so that we can say that it's true.
However, I didn't ...
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2
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Predicate logic proof solve
Provide a proof for the following using FOL in forallx
Use the natural deduction system and proof strategies in forallx to provide a formal proof for the following . Please provide a picture of your ...
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0
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0
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308
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Proving validity/invalidity of a modal argument
□(A v B) → (□A v □B) ...(1)
This symbolic argument is intuitively invalid. In (1), if we replace B with ~A, then we see that though the antecedent is necessary, the consequent is a contradiction since ...
-1
votes
1
answer
110
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Fitch proofs help?
I'm new to logic and can see how to write these out informally, but need some help seeing how they should be translated into formal proofs in Fitch.
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2
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3
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145
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Prove the following theorem: Need hints to finish it
This is not homework. I do it for fun and learning.
I use the Logic Book.
Problem has to be done in SD+.
How to prove the following argument :
|- [~A =>(~B=>C)]=>[(A v B) v (~~B v C )]
I ...
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2
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119
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Prove that the following is a logical truth (tautology) using a natural deduction derivation: (B → C) ˅ (¬B → C) [closed]
Prove that the following is a logical truth (tautology) using a natural deduction derivation:
(B → C) ˅ (¬B → C)
How do I prove this using statement logic? I know I need to start with a supposition ...
2
votes
2
answers
262
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fitch proof. P v Q, Q→ ¬ R, ¬ P, ¬ R → ¬ S GOAL: ¬ S
Need help exercise using the FITCH program format. I'm stuck on where to start. The following 4 steps must be used to prove the goal.
P v Q
Q→ ¬ R
¬ P
¬ R → ¬ S
GOAL: ¬ S
Now I know: ¬ P and P v Q ...
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votes
1
answer
188
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Solving a proof with Fitch
I'm working on an assignment and I'm stuck on this proof. I feel like I'm on the right track but I can't find the way to prove the goal.
B ^ D
(B^¬A) → ¬C
B → ¬A
(D^E)→ (A v C)
GOAL: ¬E
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votes
1
answer
601
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Complete a formal proof of ~(~A&~B) from A in as few lines as possible
Prove ~(~A&~B) from A in as few lines as possible.
~ = negation
& = conjunction
v = disjunction
| = line in a subproof
Here's what I have:
A - Premise
|~A - Assume
|~B ...
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0
votes
1
answer
384
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How do I prove :((A ⊃ B) ⊃ C) ⊃ (B ⊃ C)?
How do I prove, :((A ⊃ B) ⊃ C) ⊃ (B ⊃ C), using symbolic logic derivations where ⊃ represents a conditional i.e. A ⊃ B = A implies B?
The first line of my derivations is the assumption, (A ⊃ B) ⊃ C)....
8
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2
answers
249
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How do proofs about logic fit into a logical framework?
I'm learning logic from Michael O'Leary's A First Course in Mathematical Logic and Set Theory. In chapter 1 he carefully explains the meaning of logical implication (p ⊨ q), logical inference (p ⟹ q), ...
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2
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Fitch Proof Exercise 6.20
I am working on a proof and am stuck on a step. I am not sure why I cannot assume the negation of B. Is it not allowed or am I missing something? Thank you]1
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9
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How to prove (A v B), (A → C), (B → D) therefore (C v D)
Obviously since A → C and B → D then if A v B one of C or D must be true.
My only idea is v must be introduced, but how would I use subproofs to show one of A /\ C or B /\ D is never false if A v B?
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