@LogicPractice

Logic and applications of logic from @JohnDCook

 Houston, TX
JohnDCook.com/logic
Joined September 2016
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Big logic johndcook.com/blog/applied-l…
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An order preserving map on a complete lattice has a fixed point.
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Continuum hypothesis -- whether there a set with cardinality greater than the integers and less than the reals -- is independent of ZFC.
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Seven normal forms in logic johndcook.com/blog/seven-nor…

Logic normal forms negation, conjunction, Skolem, Blake, etc

This post discusses seven normal forms: Negation normal form Conjunctive normal form Disjunctive normal form Algebraic normal form Prefix normal form Skolem normal form Blake canonical form The photo...

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All human beings are different. All apathetic people are indifferent. Therefore, no apathetic people are human beings. -- Solomon Golomb
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Kurt Godel Created a hurdle For the truths of a system: You just can't list 'em! -- Steven Cushing
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The equivalence A ≡ B in linear logic means the formula (A ⊸ B) & (B ⊸ A) is derivable.
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Software Foundations cis.upenn.edu/~bcpierce/sf/c… #coq
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'You can sway a thousand men by appealing to their prejudices quicker than you can convince one man by logic.' -- Robert A. Heinlein
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How much can Boolean expressions be simplified? johndcook.com/blog/2020/11/1…

How much does Boolean expression minimization shorten?

If you have a Boolean function with n variables, how long can a minimized version of the expression be? How much does minimization save?

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Logic & Applications retweeted
little grey mouse 🐭@mouse_mathOct 13
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'Logic, like whiskey, loses its beneficial effect when taken in too large quantities.' -- Edward Plunkett
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Where did combinators come from? writings.stephenwolfram.com/…
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TLA: Temporal Logic of Actions research.microsoft.com/en-us…
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John D. Cook
@JohnDCookOct 8
New post: Privacy Policies and Modal Logic johndcook.com/blog/2026/10/0…
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Navier-Stokes lost in translation: Why Lean verification of AI autoformalisation does not guarantee correct natural language proofs arxiv.org/abs/2610.08144

Navier-Stokes lost in translation: Why Lean verification of AI...

Autoformalisation is increasingly used to verify mathematical texts, including those generated by AI, as in OpenAI's announced proof of blow-up of solutions to the Navier-Stokes equations. In this...

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The diamond symbol <> in modal logic can be interpreted as possibility, e.g. <>P means 'it is possible that P holds.'
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Topology Fact@TopologyFactOct 6
A topological model for provability logic johndcook.com/blog/2026/10/0…

A topological model for provability logic

Provability logic, a.k.a. Gödel-Löb logic, is a modal logic in which the box operator means a proposition is provable. It has a different topological model.

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Coq proof of Feit-Thompson theorem msr-inria.fr/news/feit-thoms…

Feit thomson proved in coq - Microsoft Research Inria Joint Centre

Home > News > Feit thomson proved in coq […]

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In linear logic, the implication A -> B can be read 'consuming A produces B.' Sometimes written with the 'lollipop' symbol for linear implication.
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Topology Fact@TopologyFactOct 4
Topological models of modal logic johndcook.com/blog/2026/10/0…

Topological models of modal logic

Topological spaces provide models of modal logics where the box operator is interpreted as the interior of a set and the diamond operator its closure.

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