diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt
index acbd407..f27f54a 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt
@@ -202,6 +202,8 @@ fun CodeViewerScreen(
     // The share of the width the left pane of a header/source pair takes.
     var splitFraction by rememberSaveable { mutableFloatStateOf(DEFAULT_SPLIT) }
     val drawerState = rememberDrawerState(DrawerValue.Closed)
+    // The sheet is shown from outside the layout below, where the jump is worked out.
+    var jumpForSheet by remember { mutableStateOf<SymbolJump?>(null) }
 
     // The other half of a header/source pair, once a wide window has asked for it and it has
     // arrived as text.
@@ -265,6 +267,27 @@ fun CodeViewerScreen(
         val sidePaneIsShown = layout == ViewerLayout.WIDE && !showsPair
         val drawerWidth = (maxWidth * DRAWER_WIDTH_FRACTION).coerceAtMost(MaxDrawerWidth)
 
+        // From a function in the outline to the same function in the other file of the pair: from
+        // a declaration in the header to its definition in the source, and back. Beside each other
+        // they already move together, so there it is not offered.
+        val jump = if (counterpartPath == null || showsPair) {
+            null
+        } else {
+            SymbolJump(
+                label = "." + counterpartPath.value.substringAfterLast('.'),
+                description = stringResource(
+                    if (cppRoleOf(counterpartPath) == CppFileRole.HEADER) R.string.codeviewer_jump_to_header else R.string.codeviewer_jump_to_source,
+                    counterpartPath.value.substringAfterLast('/'),
+                ),
+                onJump = { symbol ->
+                    outlineOpen = false
+                    scope.launch { drawerState.close() }
+                    onOpenSibling(counterpartPath, symbol.name)
+                },
+            )
+        }
+        jumpForSheet = jump
+
         val tools = ViewerTools(
             preferences = preferences,
             searching = searching,
@@ -310,6 +333,7 @@ fun CodeViewerScreen(
                             onOpenEntry = onOpenEntry,
                             onToggleFolder = onToggleFolder,
                             outlineFirst = outlineFirst,
+                            jump = jump,
                             onSwap = swapPanes,
                             onSymbolSelected = {
                                 scope.launch { drawerState.close() }
@@ -384,6 +408,7 @@ fun CodeViewerScreen(
                                 onOpenEntry = onOpenEntry,
                                 onToggleFolder = onToggleFolder,
                                 outlineFirst = outlineFirst,
+                                jump = jump,
                                 onSwap = swapPanes,
                                 onSymbolSelected = { goToSymbol(it) },
                                 modifier = Modifier.width(sidePaneWidth).fillMaxHeight(),
@@ -421,6 +446,7 @@ fun CodeViewerScreen(
     if (outlineOpen) {
         OutlineSheet(
             document = document,
+            jump = jumpForSheet,
             currentLine = firstVisibleLine,
             collapsed = collapsed,
             onToggleCollapsed = toggleCollapsed,
@@ -437,6 +463,9 @@ fun CodeViewerScreen(
     }
 }
 
+/** Goes from a function to the function of the same name in the other file of a header/source pair. */
+private class SymbolJump(val label: String, val description: String, val onJump: (CodeSymbol) -> Unit)
+
 private class ViewerTools(
     val preferences: CodeViewerPreferences,
     val searching: Boolean,
@@ -997,13 +1026,14 @@ private fun SidePane(
     onSymbolSelected: (CodeSymbol) -> Unit,
     outlineFirst: Boolean,
     onSwap: () -> Unit,
+    jump: SymbolJump?,
     modifier: Modifier = Modifier,
 ) {
     val outline = remember(document.symbols, collapsed) { outlineTree(document.symbols, collapsed) }
     val rows = remember(state.tree) { state.tree.rows() }
     val folders: @Composable (Modifier) -> Unit = { FolderCard(state, rows, onOpenFile, onToggleFolder, onOpenEntry, it) }
     val symbols: @Composable (Modifier) -> Unit = {
-        SymbolCard(document, outline, currentLine, collapsed, onToggleCollapsed, onSymbolSelected, it)
+        SymbolCard(document, outline, currentLine, collapsed, onToggleCollapsed, onSymbolSelected, jump, it)
     }
     Column(modifier.background(MaterialTheme.colorScheme.background).padding(horizontal = 10.dp, vertical = 10.dp)) {
         val half = Modifier.weight(1f).fillMaxWidth()
@@ -1065,6 +1095,7 @@ private fun SymbolCard(
     collapsed: Set<Int>,
     onToggleCollapsed: (CodeSymbol) -> Unit,
     onSymbolSelected: (CodeSymbol) -> Unit,
+    jump: SymbolJump?,
     modifier: Modifier,
 ) {
     val current = currentIn(outline, document.symbols, currentLine)
@@ -1092,6 +1123,7 @@ private fun SymbolCard(
                     isCollapsed = symbol.line in collapsed,
                     methodCount = methodCountOf(document.symbols, symbol),
                     onToggle = { onToggleCollapsed(symbol) },
+                    jump = jump,
                 ) { onSymbolSelected(symbol) }
             }
         }
@@ -1246,6 +1278,7 @@ private fun SymbolRow(
     isCollapsed: Boolean,
     methodCount: Int,
     onToggle: () -> Unit,
+    jump: SymbolJump?,
     onClick: () -> Unit,
 ) {
     val colors = rememberCodeSyntaxColors()
@@ -1311,6 +1344,22 @@ private fun SymbolRow(
                 maxLines = 1,
                 modifier = Modifier.padding(end = if (compact) 8.dp else 0.dp),
             )
+        } else if (jump != null && symbol.kind == SymbolKind.METHOD) {
+            Surface(
+                onClick = { jump.onJump(symbol) },
+                shape = RoundedCornerShape(8.dp),
+                color = MaterialTheme.colorScheme.primaryContainer,
+                contentColor = MaterialTheme.colorScheme.onPrimaryContainer,
+                modifier = Modifier.semantics { contentDescription = jump.description },
+            ) {
+                Row(
+                    Modifier.padding(start = 8.dp, end = 4.dp, top = 5.dp, bottom = 5.dp),
+                    verticalAlignment = Alignment.CenterVertically,
+                ) {
+                    Text(jump.label, fontFamily = FontFamily.Monospace, fontSize = 12.sp, fontWeight = FontWeight.Bold, maxLines = 1)
+                    UBIcon(R.drawable.ic_ub_chevron_right, null, size = 14.dp)
+                }
+            }
         } else if (!compact) {
             Text(
                 stringResource(R.string.codeviewer_outline_line, symbol.line + 1),
@@ -1326,6 +1375,7 @@ private fun SymbolRow(
 @Composable
 private fun OutlineSheet(
     document: CodeDocument,
+    jump: SymbolJump?,
     currentLine: Int,
     collapsed: Set<Int>,
     onToggleCollapsed: (CodeSymbol) -> Unit,
@@ -1400,6 +1450,7 @@ private fun OutlineSheet(
                             isCollapsed = symbol.line in collapsed,
                             methodCount = methodCountOf(document.symbols, symbol),
                             onToggle = { onToggleCollapsed(symbol) },
+                            jump = jump,
                         ) { onSymbolSelected(symbol) }
                     }
                 }
diff --git a/docs/UBGitea_기술소개.pptx b/docs/UBGitea_기술소개.pptx
index 6eef4fc..005fa20 100644
Binary files a/docs/UBGitea_기술소개.pptx and b/docs/UBGitea_기술소개.pptx differ
diff --git a/docs/development-log.md b/docs/development-log.md
index d2fd6d9..f9c35f6 100644
--- a/docs/development-log.md
+++ b/docs/development-log.md
@@ -1392,3 +1392,12 @@ This is the append-only implementation and handoff record shared by Codex and Cl
 - Live verification: installed on the SM-F966N; reproduced and fixed in unit tests only, not on
   the owner's files.
 - Next owner: the product owner, to confirm on the files they were reading.
+
+## 2026-09-28 (continued) — TASK-059: from a declaration to its definition
+
+- Request: the human product owner confirmed the C++ outline now appears, and asked to go from a
+  function in a `.h` to where it is written in the `.cpp`.
+- What changed: see `tasks/059-jump-from-declaration-to-definition.md`.
+- Checks and results: the required checks pass; 435 unit tests, 0 failures; lint 0 errors.
+- Live verification: installed on the SM-F966N; not seen on a screen by the implementer.
+- Next owner: the product owner, to confirm on the device.
diff --git a/tasks/059-jump-from-declaration-to-definition.md b/tasks/059-jump-from-declaration-to-definition.md
new file mode 100644
index 0000000..4fea9d1
--- /dev/null
+++ b/tasks/059-jump-from-declaration-to-definition.md
@@ -0,0 +1,55 @@
+# TASK-059: From a function in the header to its definition in the source
+
+Status: implemented; required checks pass; installed on the product owner's Z Fold7, awaiting their confirmation
+Owner: Claude
+Reviewer: human product owner
+
+## Outcome
+
+The human product owner confirmed the outline now appears for their C++ files (TASK-058) and asked
+whether choosing a function in a `.h` could go to where it is written in the `.cpp`.
+
+## Scope
+
+- Included: in the outline (the side pane and the outline sheet), every function of a file that
+  has a counterpart carries a button named after the counterpart's extension (`.cpp ›` in a
+  header, `.h ›` in a source file). It opens the counterpart at the function of the same name.
+  Choosing the row itself still goes to the function in the file being read.
+- Excluded:
+  - Tapping a function's name in the code itself.
+  - Side by side: the two panes already move to the same function together, so no button there.
+  - Telling overloads apart: the first function of that name is the one opened.
+
+## Writable paths
+
+- `app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt`
+- `tasks/`, `docs/`
+
+## Acceptance criteria
+
+- [x] The button appears only on functions, and only when the file has a counterpart that is not
+      already beside it.
+- [x] The drawer or sheet closes and the counterpart opens at the function.
+- [x] A function with no definition in the counterpart (inline, pure virtual) opens the counterpart
+      at its top rather than failing.
+
+## Security and privacy
+
+No additional concerns.
+
+## Required checks
+
+```text
+./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug
+```
+
+## Evidence
+
+- Required checks pass: 435 unit tests, 0 failures; lint 0 errors. No test was added: the change
+  is wiring in the screen, and the lookup it uses (`findSymbolNamed`, `openSibling` with a symbol)
+  was already covered.
+- Installed on the SM-F966N over wireless `adb`. Not seen working on a screen by the implementer.
+
+## Review findings
+
+None yet.