请帮我解答---**Extracted Content:** **Problem Number:** 4. **Question Stem (Chinese):** 如图，四边形 ABCD为正方形，DE∥AC，且 CE=CA，直线 EC交 DA延长线于 F． 求证： AE=AF． **Question Stem (English Translation):** As shown in the figure, quadrilateral ABCD is a square, DE∥AC, and CE=CA. The line EC intersects the extension of DA at F. Prove: AE=AF. **Proof Required:** AE = AF **Other Relevant Text:** 考试资料 (Exam materials / Test material) **Chart Description:** * **Type:** Geometric figure / Diagram. * **Elements:** * A square ABCD is shown. Points are labeled A, B, C, D in counter-clockwise order, starting from the top right (D is top right, C is bottom right, B is bottom left, A is top left). Note: The labels are slightly offset from the corners but clearly indicate the vertices of the square. * A diagonal AC of the square is drawn. * Point E is located to the right and below the square. * A line segment DE is drawn. * A line segment CE is drawn. * The line segment DA is extended upwards to point F. * The line EC intersects the extended line DA at point F. * Line segments AE and AF are drawn. * **Relationships:** * ABCD is a square. * DE is parallel to AC (DE∥AC). * CE is equal in length to CA (CE=CA). * F is the intersection of line EC and the extension of line DA.