diff --git a/app/src/main/java/com/lhw/pdf/MainActivity.kt b/app/src/main/java/com/lhw/pdf/MainActivity.kt
index 445e001..db4cef6 100644
--- a/app/src/main/java/com/lhw/pdf/MainActivity.kt
+++ b/app/src/main/java/com/lhw/pdf/MainActivity.kt
@@ -49,6 +49,7 @@ class MainActivity : AppCompatActivity() {
     private val presentations = mutableMapOf<Int, MyPresentation>()
     private lateinit var pdfDocument: PdfDocument
     private val showPages = mutableListOf<Boolean>()
+    private val pageGroups = mutableListOf<Int>()
     private val defaultCachedFileName = "cached.pdf"
 
     private fun setPagesPerLandscape(pages: Float) {
@@ -143,6 +144,7 @@ class MainActivity : AppCompatActivity() {
         outState.putBoolean("renderAutoCrop", renderAutoCrop)
         outState.putFloat("pagesPerLandscape", pagesPerLandscape)
         outState.putBooleanArray("showPages", showPages.toBooleanArray())
+        outState.putIntArray("pageGroups", pageGroups.toIntArray())
         outState.putFloat("thumbnailScrollProgress", thumbnailScrollProgress)
     }
 
@@ -180,15 +182,18 @@ class MainActivity : AppCompatActivity() {
 
         pdfDocument.renderThumbnails(thumbnailWidth, thumbnailHeight)
         displayManager.getDisplays(DisplayManager.DISPLAY_CATEGORY_PRESENTATION).forEach(::makePresentationView)
-
-        val bitmaps = pdfDocument.bitmapThumbnails.toSortedMap().values.toList()
+        
         showPages.clear()
-        bitmaps.forEach { _ -> showPages.add(true) }
-        savedInstanceState?.getBooleanArray("showPages")?.forEachIndexed { i, show ->
-            showPages[i] = show
+        pageGroups.clear()
+        (0..<pdfDocument.numPages).forEach {
+            showPages.add(true)
+            pageGroups.add(it)
         }
+        savedInstanceState?.getBooleanArray("showPages")?.forEachIndexed { i, show -> showPages[i] = show }
+        savedInstanceState?.getIntArray("pageGroups")?.forEachIndexed { i, groupIdx -> pageGroups[i] = groupIdx }
         viewModel.showPages.value = showPages.toList()
-        viewModel.pageThumbnails.value = bitmaps
+        viewModel.pageGroups.value = pageGroups.toList()
+        viewModel.pageThumbnails.value = pdfDocument.bitmapThumbnails.toSortedMap().values.toList()
 
 
         viewModel.pagesPerLandscape.observe(this) {
diff --git a/app/src/main/java/com/lhw/pdf/PdfDocument.kt b/app/src/main/java/com/lhw/pdf/PdfDocument.kt
index 4c0342d..e42fa63 100644
--- a/app/src/main/java/com/lhw/pdf/PdfDocument.kt
+++ b/app/src/main/java/com/lhw/pdf/PdfDocument.kt
@@ -32,7 +32,7 @@ class PdfDocument(private val fileCached: File, var usePdfBox: Boolean = true, p
     private val autoCropSafetyMarginUpper = 2
     private val autoCropSafetyMarginLower = 16
 
-    private val numPages get() = if (usePdfBox) pdfDocument.numberOfPages else renderer.pageCount
+    val numPages get() = if (usePdfBox) pdfDocument.numberOfPages else renderer.pageCount
 
     init {
         for (i in 0..<numPages) {
diff --git a/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryFragment.kt b/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryFragment.kt
index 75b3d9e..d08579a 100644
--- a/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryFragment.kt
+++ b/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryFragment.kt
@@ -30,8 +30,6 @@ class GalleryFragment : Fragment() {
         container: ViewGroup?,
         savedInstanceState: Bundle?
     ): View {
-//        val galleryViewModel = ViewModelProvider(this)[GalleryViewModel::class.java]
-
         _binding = FragmentGalleryBinding.inflate(inflater, container, false)
         binding.viewModel = galleryViewModel
         val root: View = binding.root
diff --git a/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryViewModel.kt b/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryViewModel.kt
index fb46b90..e628b07 100644
--- a/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryViewModel.kt
+++ b/app/src/main/java/com/lhw/pdf/ui/gallery/GalleryViewModel.kt
@@ -8,6 +8,7 @@ import androidx.lifecycle.ViewModel
 class GalleryViewModel : ViewModel() {
     val pageThumbnails = MutableLiveData<List<Bitmap>>().apply { value = listOf() }
     val showPages = MutableLiveData<List<Boolean>>().apply { value = listOf() }
+    val pageGroups = MutableLiveData<List<Int>>().apply { value = listOf() }
     val thumbnailScrollProgress = MutableLiveData<Float>().apply { value = 0F }
     val textDisplays = MutableLiveData<String>().apply { value = "" }
     val pagesPerLandscape = MutableLiveData<Float>().apply { value = 3F }
diff --git a/app/src/main/java/com/lhw/pdf/ui/home/HomeFragment.kt b/app/src/main/java/com/lhw/pdf/ui/home/HomeFragment.kt
index fed8f43..1036c59 100644
--- a/app/src/main/java/com/lhw/pdf/ui/home/HomeFragment.kt
+++ b/app/src/main/java/com/lhw/pdf/ui/home/HomeFragment.kt
@@ -1,15 +1,23 @@
 package com.lhw.pdf.ui.home
 
+import android.graphics.Bitmap
 import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.widget.ImageView
+import android.widget.LinearLayout
 import android.widget.TextView
+import androidx.core.view.children
 import androidx.fragment.app.Fragment
+import androidx.fragment.app.activityViewModels
 import androidx.lifecycle.ViewModelProvider
 import com.lhw.pdf.databinding.FragmentHomeBinding
+import com.lhw.pdf.ui.gallery.GalleryViewModel
 
 class HomeFragment : Fragment() {
+    private val galleryViewModel: GalleryViewModel by activityViewModels()
+    private val thumbnailImageViews = mutableListOf<ImageView>()
 
     private var _binding: FragmentHomeBinding? = null
 
@@ -22,16 +30,11 @@ class HomeFragment : Fragment() {
         container: ViewGroup?,
         savedInstanceState: Bundle?
     ): View {
-        val homeViewModel =
-            ViewModelProvider(this)[HomeViewModel::class.java]
-
         _binding = FragmentHomeBinding.inflate(inflater, container, false)
         val root: View = binding.root
 
-        val textView: TextView = binding.textHome
-        homeViewModel.text.observe(viewLifecycleOwner) {
-            textView.text = it
-        }
+        galleryViewModel.pageThumbnails.observe(viewLifecycleOwner, ::populateThumbnails)
+
         return root
     }
 
@@ -39,4 +42,48 @@ class HomeFragment : Fragment() {
         super.onDestroyView()
         _binding = null
     }
+
+    private fun reLayoutThumbnails() {
+        val container = binding.thumbnailsLayout
+        container.children.forEach { (it as LinearLayout).removeAllViewsInLayout() }
+        container.removeAllViewsInLayout()
+        val groupContainers = mutableMapOf<Int, LinearLayout>()
+        galleryViewModel.pageGroups.value?.forEachIndexed {i, groupIdx ->
+            if (groupIdx !in groupContainers) {
+                val c = LinearLayout(context)
+                groupContainers[groupIdx] = c
+                container.addView(c)
+            }
+            groupContainers[groupIdx]?.addView(thumbnailImageViews[i])
+        }
+    }
+
+    private fun populateThumbnails(bitmaps: List<Bitmap>) {
+        bitmaps.forEachIndexed() { index, bitmap ->
+            val img = ImageView(context)
+            img.setImageBitmap(bitmap)
+            if (index > 0) {
+                img.setOnClickListener {
+                    val pageGroups = galleryViewModel.pageGroups.value!!.toMutableList()
+                    val oldGroup = pageGroups[index]
+                    if (oldGroup > pageGroups[index-1]) {  // Merge with previous group
+                        val newGroup = pageGroups[index-1]
+                        pageGroups[index] = newGroup
+                        pageGroups.forEachIndexed { i, value ->
+                            if (value == oldGroup) pageGroups[i] = newGroup
+                        }
+                    } else {  // Escape group into original number, taking trailing members with it
+                        pageGroups[index] = index
+                        pageGroups.forEachIndexed { i, value ->
+                            if ((value == oldGroup) and (i > index)) pageGroups[i] = index
+                        }
+                    }
+                    galleryViewModel.pageGroups.value = pageGroups.toList()
+                    reLayoutThumbnails()
+                }
+            }
+            thumbnailImageViews.add(img)
+        }
+        reLayoutThumbnails()
+    }
 }
\ No newline at end of file
diff --git a/app/src/main/res/layout/fragment_home.xml b/app/src/main/res/layout/fragment_home.xml
index f3d9b08..d5c6d63 100644
--- a/app/src/main/res/layout/fragment_home.xml
+++ b/app/src/main/res/layout/fragment_home.xml
@@ -6,17 +6,17 @@
     android:layout_height="match_parent"
     tools:context=".ui.home.HomeFragment">
 
-    <TextView
-        android:id="@+id/text_home"
+    <ScrollView
+        android:id="@+id/thumbnails_scroll"
         android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:layout_marginStart="8dp"
-        android:layout_marginTop="8dp"
-        android:layout_marginEnd="8dp"
-        android:textAlignment="center"
-        android:textSize="20sp"
-        app:layout_constraintBottom_toBottomOf="parent"
-        app:layout_constraintEnd_toEndOf="parent"
-        app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toTopOf="parent" />
+        android:layout_height="match_parent"
+        android:layout_weight="3">
+
+        <LinearLayout
+            android:id="@+id/thumbnails_layout"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:orientation="vertical"
+            tools:showIn="@layout/content_main" />
+    </ScrollView>
 </androidx.constraintlayout.widget.ConstraintLayout>
\ No newline at end of file