d="smooth">
                        <figure>
                            <img src="../images/chp04/smooth.svg" alt="Smooth curve and Tangent vector" title="Smooth curve and Tangent vector" style="width:100%;">
                            <figcaption>
                                $z'(t)=x'(t) + iy(t)$ as a tangent vector.
                            </figcaption>
                        </figure>
                    </div>
                    <div id="not-smooth">
                        <figure>
        