Category
Logic
Quantifiers, contrapositives, and arguments that hold up.
Logic is the grammar of proof. Every other category leans on it, and it is worth practising on its own, where the reasoning is the entire content of the problem rather than the scaffolding around it.
You will find propositional and predicate logic, negation and contraposition, quantifier order, truth tables, and puzzles about consistent and inconsistent statements. Precision matters more than speed here.
Latest problems
40 problems
Eight People's Birthdays
908
57
Plants in an Orchard
1387
23
Ferry Trips for a Wolf, a Goat, and a Cabbage
1050
33
Five Doors, One Switch
1317
27
Five Rational Pirates
1738
28
Four Ages in a Row
988
47
Knights and Knaves
1280
31
Maximizing a Partial Sum
1098
47