diff --git a/w5/diagram.svg b/w5/diagram.svg
new file mode 100644
index 0000000..d283d71
--- /dev/null
+++ b/w5/diagram.svg
@@ -0,0 +1,77 @@
+<svg width="100%" viewBox="0 0 680 520" xmlns="http://www.w3.org/2000/svg">
+<defs>
+  <marker id="arrow" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="8" markerHeight="8" orient="auto-start-reverse">
+    <path d="M2 1L8 5L2 9" fill="none" stroke="context-stroke" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </marker>
+  <marker id="inherit" viewBox="0 0 12 12" refX="10" refY="6" markerWidth="10" markerHeight="10" orient="auto">
+    <polygon points="2,2 10,6 2,10" fill="none" stroke="context-stroke" stroke-width="1.5" stroke-linejoin="round"/>
+  </marker>
+</defs>
+
+<!-- Shape (abstract class) -->
+<g style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto">
+  <rect x="240" y="30" width="200" height="90" rx="8" stroke-width="1" style="fill:rgb(238, 237, 254);stroke:rgb(83, 74, 183);color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="58" text-anchor="middle" dominant-baseline="central" style="fill:rgb(60, 52, 137);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:14px;font-weight:500;text-anchor:middle;dominant-baseline:central">«abstract»</text>
+  <text x="340" y="78" text-anchor="middle" dominant-baseline="central" style="fill:rgb(60, 52, 137);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:14px;font-weight:500;text-anchor:middle;dominant-baseline:central">Shape</text>
+  <line x1="240" y1="92" x2="440" y2="92" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="107" text-anchor="middle" dominant-baseline="central" style="fill:rgb(83, 74, 183);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">+ getArea() : double</text>
+</g>
+
+<!-- Inheritance arrows (hollow triangle heads) -->
+<!-- Circle -->
+<line x1="120" y1="220" x2="270" y2="122" stroke="var(--color-border-primary)" stroke-width="1.5" marker-end="url(#inherit)" fill="none" style="fill:none;stroke:rgba(31, 30, 29, 0.4);color:rgb(0, 0, 0);stroke-width:1.5px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+<!-- Rectangle -->
+<line x1="340" y1="220" x2="340" y2="122" stroke="var(--color-border-primary)" stroke-width="1.5" marker-end="url(#inherit)" style="fill:rgb(0, 0, 0);stroke:rgba(31, 30, 29, 0.4);color:rgb(0, 0, 0);stroke-width:1.5px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+<!-- Triangle -->
+<line x1="562" y1="220" x2="415" y2="122" stroke="var(--color-border-primary)" stroke-width="1.5" marker-end="url(#inherit)" style="fill:rgb(0, 0, 0);stroke:rgba(31, 30, 29, 0.4);color:rgb(0, 0, 0);stroke-width:1.5px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+
+<!-- Circle class -->
+<g style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto">
+  <rect x="30" y="220" width="180" height="110" rx="8" stroke-width="1" style="fill:rgb(225, 245, 238);stroke:rgb(15, 110, 86);color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="120" y="248" text-anchor="middle" dominant-baseline="central" style="fill:rgb(8, 80, 65);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:14px;font-weight:500;text-anchor:middle;dominant-baseline:central">Circle</text>
+  <line x1="30" y1="262" x2="210" y2="262" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="120" y="280" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">- radius : double</text>
+  <line x1="30" y1="294" x2="210" y2="294" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="120" y="314" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">+ getArea() : double</text>
+</g>
+
+<!-- Rectangle class -->
+<g style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto">
+  <rect x="240" y="220" width="200" height="110" rx="8" stroke-width="1" style="fill:rgb(225, 245, 238);stroke:rgb(15, 110, 86);color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="248" text-anchor="middle" dominant-baseline="central" style="fill:rgb(8, 80, 65);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:14px;font-weight:500;text-anchor:middle;dominant-baseline:central">Rectangle</text>
+  <line x1="240" y1="262" x2="440" y2="262" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="276" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">- width : double</text>
+  <text x="340" y="292" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">- height : double</text>
+  <line x1="240" y1="306" x2="440" y2="306" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="322" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">+ getArea() : double</text>
+</g>
+
+<!-- Triangle class -->
+<g style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto">
+  <rect x="460" y="220" width="190" height="110" rx="8" stroke-width="1" style="fill:rgb(225, 245, 238);stroke:rgb(15, 110, 86);color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="555" y="248" text-anchor="middle" dominant-baseline="central" style="fill:rgb(8, 80, 65);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:14px;font-weight:500;text-anchor:middle;dominant-baseline:central">Triangle</text>
+  <line x1="460" y1="262" x2="650" y2="262" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="555" y="276" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">- base : double</text>
+  <text x="555" y="292" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">- height : double</text>
+  <line x1="460" y1="306" x2="650" y2="306" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="555" y="322" text-anchor="middle" dominant-baseline="central" style="fill:rgb(15, 110, 86);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">+ getArea() : double</text>
+</g>
+
+<!-- ShapeUtil class -->
+<g style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto">
+  <rect x="240" y="400" width="200" height="90" rx="8" stroke-width="1" style="fill:rgb(250, 238, 218);stroke:rgb(133, 79, 11);color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="424" text-anchor="middle" dominant-baseline="central" style="fill:rgb(99, 56, 6);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:14px;font-weight:500;text-anchor:middle;dominant-baseline:central">ShapeUtil</text>
+  <line x1="240" y1="438" x2="440" y2="438" stroke-width="0.8" opacity="0.5" style="fill:rgb(0, 0, 0);stroke:none;color:rgb(0, 0, 0);stroke-width:0.8px;stroke-linecap:butt;stroke-linejoin:miter;opacity:0.5;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+  <text x="340" y="452" text-anchor="middle" dominant-baseline="central" style="fill:rgb(133, 79, 11);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">«static»</text>
+  <text x="340" y="470" text-anchor="middle" dominant-baseline="central" style="fill:rgb(133, 79, 11);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:middle;dominant-baseline:central">+ printArea(shape: Shape)</text>
+</g>
+
+<!-- ShapeUtil uses Shape (dashed arrow) -->
+<line x1="340" y1="400" x2="340" y2="332" stroke="var(--color-border-primary)" stroke-width="1.2" stroke-dasharray="6,4" marker-end="url(#arrow)" style="fill:rgb(0, 0, 0);stroke:rgba(31, 30, 29, 0.4);color:rgb(0, 0, 0);stroke-width:1.2px;stroke-dasharray:6px, 4px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+
+<!-- Legend -->
+<line x1="40" y1="430" x2="80" y2="430" stroke="var(--color-border-primary)" stroke-width="1.5" marker-end="url(#inherit)" style="fill:rgb(0, 0, 0);stroke:rgba(31, 30, 29, 0.4);color:rgb(0, 0, 0);stroke-width:1.5px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+<text x="90" y="434" dominant-baseline="central" style="fill:rgb(61, 61, 58);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:start;dominant-baseline:central">继承关系</text>
+<line x1="40" y1="460" x2="80" y2="460" stroke="var(--color-border-primary)" stroke-width="1.2" stroke-dasharray="6,4" marker-end="url(#arrow)" style="fill:rgb(0, 0, 0);stroke:rgba(31, 30, 29, 0.4);color:rgb(0, 0, 0);stroke-width:1.2px;stroke-dasharray:6px, 4px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:16px;font-weight:400;text-anchor:start;dominant-baseline:auto"/>
+<text x="90" y="464" dominant-baseline="central" style="fill:rgb(61, 61, 58);stroke:none;color:rgb(0, 0, 0);stroke-width:1px;stroke-linecap:butt;stroke-linejoin:miter;opacity:1;font-family:&quot;Anthropic Sans&quot;, -apple-system, BlinkMacSystemFont, &quot;Segoe UI&quot;, sans-serif;font-size:12px;font-weight:400;text-anchor:start;dominant-baseline:central">依赖/使用关系</text>
+</svg>
\ No newline at end of file