LogicPuzzles.io offers 12 Nikoli-style logic puzzle types playable free in a browser with no account required. Every puzzle is algorithmically generated and verified to have exactly one logical solution, with features including pencil marks, undo, instant checking, daily challenges, and progress tracking.
All/Some is a free web-based logic puzzle game about set relationships using Euler diagrams, created by a husband-and-wife team. The game originated from a viral Instagram puzzle and now offers daily free challenges plus themed collections for paid members. The creators seek feedback on puzzle format variations and membership pricing.
This paper proves that Zermelo-Fraenkel set theory (ZF) is consistent within the type theory of Lean, using only excluded middle and no additional axioms like choice or propositional extensionality. The proof employs large elimination of the accessibility predicate to construct ordinals and validate the Replacement axiom, showing that ZF has a model in this type-theoretic framework.