# The prompt — identical for all four models

> Build a single, self-contained HTML file (inline CSS and JavaScript, zero external dependencies, no CDN imports) that visualizes the Fourier series approximation of a square wave using rotating epicycles. Rotating circles, each one a term in the series, with the tip of the chain tracing a square wave in real time. Include a slider for the number of terms (1–50), a speed control, a pause button, and a live mean-squared-error readout comparing the traced wave to an ideal square wave.

Rules of the run:

- One prompt. One file each. **No back-and-forth.**
- Whatever came out on the first real pass is what ships.
- The MSE readout is the referee — a correctness check baked into the deliverable itself.