Games Like Quod Erat Demonstrandum

About Quod Erat Demonstrandum

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 — step by step — until you reach the conclusion. Each level is a proof waiting to be completed.

As a newly aware intelligence, each proof explores themes of being and essence, virtue, the soul, causality, and the pursuit of truth. Simply put, you are a mind reasoning its way from first principles toward understanding.

Features

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120+ handcrafted levels spanning propositional logic and predicate calculus, levels varying both thematically and mechanically

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23 rules of logic — 7 rules of inference (Modus Ponens, Modus Tollens, Hypothetical Syllogism, and more), 11 rules of replacement (Double Negation, De Morgan's Laws, Transposition, and more), and 5 quantifier rules (Universal/Existential Instantiation and Generalization, Quantifier Negation)

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Gentle learning curve — 18 tutorial levels introduce one rule at a time, building from simple one-step proofs to multi-step chains

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Deep complexity — later levels feature nested quantifiers, multi-variable domains, and proofs requiring 10+ derivation steps

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Intuitive drag-and-drop interface — slot propositions into rules, see the result, and build your proof step by step

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Par system — every level has an optimal solution length; can you find the shortest proof?

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No time pressure — think as long as you need; every proof waits for you

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60+ Steam achievements — milestones, rule mastery challenges, and hidden achievements for completionists