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Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

🕹️ Practice arcade

Extra games, not extra homework — timed sprints, survival runs that end when your lives run out, and mastery drills built from the same skills Discrete Mathematics II — Combinatorics teaches.

Log in to play — the arcade tracks runs per student.

⚡ Sprints

Beat the clock.

🔄 Arrangements & Distributions Sprint

Count circular arrangements, multiset permutations, stars-and-bars splits, compositions, lattice paths, and Catalan numbers — 90 seconds.

⚡ Counting Toolkit Sprint

Ninety seconds of product-rule, sum-rule, permutation, and combination counts — as many as you can.

🎲 Pascal's Rule & Combinations Sprint

Apply Pascal's identity to a binomial coefficient, or count an unordered selection directly.

🔄 Euler Circuit Sprint

A connected graph has an Euler circuit only when every vertex has even degree -- check as many as you can.

🎯 Mastery

No clock — just get N in a row.

📦 Distribution Case Recognition Mastery

Read a scenario and name which of the four objects-identical / boxes-identical cases it models.

🎯 Multiset Arrangements Mastery

Count arrangements of a multiset (repeated letters and all) correctly four times in a row.