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

prediction

A guess produced by a fixed rule from facts already known, written $\hat{y}$ ; the truth it is compared against later is $y$ .

Examples

The rule $\hat{y} = 26 - 2x$ predicts 14 for a car with $x = 6$ ; the car later sells for $y = 17$ .