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Discover the challenging fun of validating logical proofs, beginning with simple propositional calculus and ending with complex, multi-domain predicate calculus. Prove yourself to be a master of logical thinking!
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Every argument begins with set of premises that, if true, necessitate some conclusion. Your task is to prove that the conclusion does indeed follow.
Given a set of premises, apply rules of inference and replacement to derive new propositions until you reach the conclusion. Each level is a proof waiting to be completed.
Explore philosophical themes grounded in the works of Plato, Aristotle, St. Thomas Aquinas, and more! Though be prepared: while the levels start off easy and resemble the sort of proofs you might encounter in the wild, they soon evolve to challenge your logical thinking and pattern recognition abilities.
180+ handcrafted levels spanning propositional logic and predicate calculus, levels varying both thematically and mechanically
23 rules of logic — 7 rules of inference (e.g., Modus Ponens, Modus Tollens, Hypothetical Syllogism), 11 rules of replacement (e.g., Double Negation, De Morgan's Laws, Transposition), and 5 quantifier rules (Universal/Existential Instantiation and Generalization, Quantifier Negation)
Gentle learning curve — 23 tutorial levels introduce one rule at a time, building from simple one-step proofs to multi-step chains
Deep complexity — later levels feature nested quantifiers, multi-variable domains, and proofs requiring many steps involving complex statements
Par system — every level has an optimal solution length; can you find the shortest proof?
No time pressure — think as long as you need, a par score isn't needed to beat the game
60+ Steam achievements — milestones, rule mastery challenges, and other fun achievements for completionists
Cloud saves — pick up where you left off on any machine
Quod Erat Demonstrandum costs $2.63 right now. That's 12% off the regular price of $2.99.
Based on Wish9's price records and IsThereAnyDeal history, the lowest price is $2.63.
The current price ($2.63) is at or very close to the lowest price on record. It has gone on sale 1 time in the past year. The next big Steam sale, the Steam Winter Sale, starts in 34 days. This is for reference, based on past price records, and doesn't guarantee future prices.
Recommended: Graphics card Integrated graphics, Processor 2.0 GHz dual-core, Memory 4 GB RAM. Minimum: Graphics card Integrated graphics, Processor 1.6 GHz dual-core, Memory 4 GB RAM. Save your PC specs on Wish9 to compare them with this game instantly.
