Construct a proof one justified line at a time, every step must follow from what's already on the ledger, and any logical leap is thrown out.
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How to play
The left pane shows the figure, the givens and the goal. The center is a two-column ledger of statement and justification that you build. From the pool of candidate steps, add one at a time; a step is accepted only when its prerequisites are already proven. Derive the goal to complete the proof.
Click a candidate step to try adding it to the ledger
Steps lock until their prerequisite lines are established
Invalid leaps are rejected, sometimes with a counterexample
Reach the goal in fewer lines, with fewer hints, for a higher score
Game modes
Daily: a fixed proof shared each day
Practice: fresh randomized problems
Controls
Desktop: click steps in the pool to add them; Undo, Hint and New are on the toolbar
Phone & tablet: tap a step to add it and tap the toolbar buttons (mouse or touch only)
Tips & strategy
Work forward from the givens, look for the step whose prerequisites you already have on the ledger
Use hints sparingly; each one places the next canonical line but lowers your final score
What you'll learn
Lemma teaches rigorous deductive proof, enforcing that every step is justified.
Lemma is an original free browser logic game that teaches rigorous deductive proof, enforcing that every claim be justified by prior lines just as a real two-column geometry proof demands.
A free, original browser game on PlayPendium. No download, no install.
