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

• 120+ handcrafted levels spanning propositional logic and predicate calculus, levels varying both thematically and mechanically
• 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)
• Gentle learning curve — 18 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 10+ derivation steps
• Intuitive drag-and-drop interface — slot propositions into rules, see the result, and build your proof step by step
• Par system — every level has an optimal solution length; can you find the shortest proof?
• No time pressure — think as long as you need; every proof waits for you
• 60+ Steam achievements — milestones, rule mastery challenges, and hidden achievements for completionists
• Cloud saves — pick up where you left off on any machine