or(var j = 1; j < w; ++j){
        x1 = chebyshev_client_to_x(j-1);
        x2 = chebyshev_client_to_x(j);
        y1 = polynomial_in_x(X, x1, chebyshev_n);
        y2 = polynomial_in_x(X, x2, chebyshev_n);
        chebyshev_context.moveTo(chebyshev_x_to_client(x1), chebyshev_y_to_client(y1));
        chebyshev_context.lineTo(chebyshev_x_to_client(x2), chebyshev_y_to_client(y2));
    }
    chebyshev_context.strokeStyle="#661100";
    chebyshev_context.stroke();
    chebyshev_context.closePath();

    // dot