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- ∃x (P (x) → ∀y P (y)) September 19, 2024(a) Let the domain consist of all people in a pub and P (x) denote the statement that x is drinking. Briefly argue whether this statement is always true or not. ∃x (P (x) → ∀y P (y)) The statement means there is someone in the pub such that, if he or she is drinking, […]Dasiy
- Question About Gödel's Second Incomplete Theorem September 19, 2024I'm trying to understand the statement of Gödel's second incompleteness theorem. For a set of axioms $\Phi$ containing $\Phi_{PA}$, the author claims the following sentence 'express' the consistency of $\Phi$: $$Con(\Phi) := \neg Prov_\Phi(0\equiv 1)$$ My question is: what is the precise relationship between consistency of $\Phi$ and the sentence $Con(\Phi)?$ My guess is Maybe […]Hydrogen
- Why is Abstract Algebraic Logic not as useful for predicate logics? September 19, 2024I have read multiple times that the tools of Abstract Algebraic Logic are most useful only when restricted to propositional logics, meaning that they are much less useful in predicate logics. Is that so? In what sense are the algebraic tools less useful? Could you give me some intuitive explanation as to why is that? […]kevin.spacey
- Determining truth values September 18, 2024I know this might sound extremely basic, but I'm currently in discrete math and we are learning logic. I'm actually having a really hard time with questions that ask me to determine the truth value of certain expressions. The one in particular is the following:$$x = 2^4.$$ Apparently this is not a statement, but I'm […]Oldmathdude
- I’m trying to understand how to calculate this proof. [closed] September 18, 2024Im am trying to understand how to solve this proof and my professor said that we cannot use repetition $P \vdash P$.Mikayla Ruff
- The necessary condition in the implication "$p\Rightarrow q$" [duplicate] September 18, 2024My understanding is that in the implication $$p {\implies} q,$$ $p$ is sufficient to conclude $q$, and $q$ is necessary condition for $p$. Let $p$ be "it is raining," and $q$ be "the sidewalk is wet." The sufficient condition statement "If it is raining then it is sufficient to conclude that the sidewalk is wet" […]novice programmer
- Are there consequences to assuming that there are only a certain class of inductively defined functions on any given set? September 17, 2024On any set $X$, it seems intuitive that the only functions $X^n \to X$ we can actually specify are those which follow structurally from, say, the axioms of ZFC. In particular, it seems highly intuitive that this class of functions that can actually be written down is some near-inductively defined set of functions such as […]William Oliver
- Conditional or biconditional for 'except'? September 17, 2024The following translation is given in (part (c) of Q1 of Exercise 2.1 in) the book How to Prove It by Daniel Velleman: Everyone likes Mary, except Mary herself. $$\forall x(\neg(x=m)\rightarrow L(x, m)),$$ where $L(x, y)$ stands for "$x$ likes $y$" and $m$ for "Mary". Acording to this formalisation, $L(m, m)$ is possible. But, according […]Muhammad Safiullah
- Is second-order arithmetic subject to Gödel's first incompleteness theorem? If so, why is it? September 17, 2024I have studied Gödel's first incompleteness theorem for first-order logic (FOL) and believe I grasp the proof. The theorem implies the existence of non-standard models for Peano arithmetic. I also heard that second-order arithmetic is categorical, meaning that all its models are isomorphic. My question is: Is second-order arithmetic subject to Gödel's first incompleteness theorem? […]Victor
- Is “reduct” just another word for “image through a forgetful functor”? September 17, 2024I have just started learning Mathematical Logic in greater depth and I was assigned some lecture notes to read. I noticed how the lecturer often used the word reduct, to mean… a structure which has gone through a transformation, I guess. I’ll give you one example: he had just finished introducing Gödel Algebras, and in […]Melanzio
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