// Finished in earlier steps.
export type Vec = { x: number; y: number };
export const vec = (x: number, y: number): Vec => ({ x, y });
export const sub = (a: Vec, b: Vec): Vec => ({ x: a.x - b.x, y: a.y - b.y });
export const scale = (a: Vec, s: number): Vec => ({ x: a.x * s, y: a.y * s });
export const dot = (a: Vec, b: Vec): number => a.x * b.x + a.y * b.y;