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first-order and higher-order logic, model theory, set theory, proof theory, computability theory, formal languages, definability, interplay of syntax and semantics, constructive logic, intuitionism, philosophical logic, modal logic, completeness, Gödel incompleteness, decidability, undecidability, theories of truth, truth revision, consistency.
20
votes
What is neutral constructive mathematics
You'll probably have better luck with the phrase "intuitionistic higher-order logic" (IHOL). A good place to start is the book by Lambek and Scott, Introduction to Higher Order Categorical Logic. But …
8
votes
Categories of recursive functions
Regarding question 1.: it's hard to find the statement spelled out in black and white in the literature. Apparently Gavin Wraith proved it in unpublished notes titled "Notes on arithmetic universes an …
10
votes
Accepted
Primitive recursive arithmetic via universal algebra
According to unpublished notes by Gavin Wraith ("Notes on arithmetic universes and Gödel incompleteness theorems" (1985)), PRA can be described as an equational theory or as a Lawvere theory, and is a …
7
votes
Accepted
What is some good introduction to lambda calculus?
There is, of course, the very famous book by Barendregt,
The Lambda Calculus, Its Syntax and Semantics (Studies in Logic and the Foundations of Mathematics, Volume 103). Revised Edition, North-Holl …
3
votes
Does the exact pair phenomenon for partial orders occur in your area of mathematics?
In trying to understand better a certain weak choice axiom, I once concocted an example in sheaf theory which involves an exact pair in the sense of this question, without knowing it was a "thing" els …
15
votes
Accepted
Logical complexity of algebraically closed fields
From Dirk van Dalen's Logic and Structure: the theory of algebraically closed fields is not finitely axiomatizable (see page 109 and preceding).
2
votes
In which sense "closure" is a closure?
Actually, there is a topological meaning to closure of logical formulas, if one represents formulas by string diagrams. A description of such a string diagram calculus, interpreting Peirce's existenti …
38
votes
5
answers
5k
views
Does "compact iff projections are closed" require some form of choice?
There are many equivalent ways of defining the notion of compact space, but some require some kind of choice principle to prove their equivalence. For example, a classical result is that for $X$ to be …
2
votes
Injecting premises into two implicational premises connected by a tensor (multiplicative con...
Well, this is very easy, but because linear logic might be considered a little too specialized for Mathematics StackExchange, I'll answer.
Since the natural semantics of MLL (multiplicative linear l …
18
votes
Is there a natural bijection from $\mathbb{N}$ to $\mathbb{Q}$?
To my aesthetic sensibilities, the Calkin-Wilf tree response is pretty close to optimal, but I'll add some additional glosses. (I only noticed later that Vladimir Dotsenko wrote something similar befo …
4
votes
Brouwer vs. Cantor
Troelstra is a well-known exponent of intuitionism. Here are two online articles that contain philosophical and historical material that may be useful to you:
Remarks on Intuitionism and the Philos …
1
vote
Self-similarity for simple algebraic structures
I haven't read your description (and don't know the area well enough) to make an evaluation, but as far as algebraic treatments go... have you seen Tom Leinster's Theory of Self-Similarity? This is ba …
3
votes
"Introduction to mathematical logic" book from a formalist perspective
I don't know of logic textbooks which adopt an explicitly formalist viewpoint (which is not to say I think none exist), but for what it's worth, I'd say that books on categorical logic tend not to ado …
44
votes
Accepted
Completion of a category
Yes, it's a general construction which is related to so-called Isbell conjugation.
Let $C$ be a small category. It is well-known that the free colimit cocompletion is given by the Yoneda embedding i …
8
votes
Accepted
Adjoining an arrow to a CCC
They mean this: given a cartesian closed $\mathcal{A}$ and objects $A, B$ of $\mathcal{A}$, the inclusion $i: \mathcal{A} \to \mathcal{A}[x]$ is universal with respect to strict cartesian closed funct …