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Jan
21
comment Proof in Propositional Logic of Peirce's Law
I don't see how you got to step 8.
Dec
18
comment Propositional formulas 3
It does associate in the sense that for whatever truth value ((A↔B)↔C) has, (A↔(B↔C)) has the same truth value also.
Dec
18
comment Propositional formulas 3
A↔B↔C makes for a relatively poor example, since ↔ associates.
Dec
15
comment For a homework, how do i use resolution to prove G
How is ∀x∃yR(x,y) not in prenex normal form? Do you know how to find a unifier, substitute, cancel out terms, and then take a disjunction?
Dec
10
comment Is it possible for there to be a mechanical way in which one would prove a tautology (in a propositional calculus)
@Stacked I take that back about no algorithm existing for formal proofs. There often enough does exist the possibility of doing what can get called a level saturation search. It depends on what we want to prove as to whether that comes as interesting or not. Often enough a level saturation search isn't all that interesting, though it can be.
Dec
10
revised Is it possible for there to be a mechanical way in which one would prove a tautology (in a propositional calculus)
added 28 characters in body
Dec
9
comment Is it possible for there to be a mechanical way in which one would prove a tautology (in a propositional calculus)
"Yes, there are a few methods: truth tables, axiomatic (or "Hilbert-style") systems, natural deduction, and others." Axiomatic systems don't provide an algorithm for proofs from the axioms. And what if the propositional calculus only has infinite valued models, such as Lukasiewicz infinite-valued logic?
Dec
9
answered Is it possible for there to be a mechanical way in which one would prove a tautology (in a propositional calculus)
Dec
9
revised what are the Rosser Turquette axioms of Lukasiewicz 3 valued propositional logic?
edited body
Nov
25
answered How can I solve this logic question using propositional logic (Natural deduction)?
Nov
25
answered converting predicate logic to clause form
Nov
24
revised Is Negation of $(a \implies \neg b)$ Equivalent to $(a \implies b)$?
edited body
Nov
21
answered Equivalence between fragments of intuitionistic and classical logics
Nov
17
comment Equivalence between fragments of intuitionistic and classical logics
"The two logics are equivalent for the {∧,∨}{∧,∨} fragment, though." There don't exist any theorems in that fragment. Note that the question makes reference to a formula as "proofable" [sic]. So, yes, they are equivalent.
Nov
16
comment Why the ordering of the quantifiers matters here?
"Now I know that the correct form is ∃T∀Xfool(X,T)∃T∀Xfool(X,T)." There exists a time such that for all people, I fool person X at that time. There is no "can" here, unlike your original statement.
Nov
16
comment Can the negation of an implication statement be written in terms of implication operators?
@NoahSchweber You might speak correctly, but I can't tell at this point in time.
Nov
16
comment Proof that this equation is correct
What does it mean for two truths to be equal? The truths "usually grass looks green," and "the Earth revolves around the sun", I think, have the same truth value. But do those truths stand as equal?
Nov
15
answered How to prove D70 = {1, 2, 5, 7, 10, 14, 35, 70} is a Boolean algebra
Nov
14
answered Can the negation of an implication statement be written in terms of implication operators?
Nov
14
answered Is the following a unifier, but not a most general unifier?