diff --git a/0006-on.mouse_press b/0006-on.mouse_press
index 7a086b1..2a241f8 100644
--- a/0006-on.mouse_press
+++ b/0006-on.mouse_press
@@ -1,18 +1,8 @@
 on.mouse_press = function(x,y, mouse_button)
-	if Cursor_node then
-		Cursor_node.show_cursor = nil
-		Cursor_node = nil
-	end
-	if mouse_press_consumed_by_any_button_handler(HUD, x,y, mouse_button) then
+	if mouse_press_consumed_by_any_button_handler(Global_state, x,y, mouse_button) then
 		return
 	end
-	local node = on_text(x,y)
-	if node then
-		-- position cursor in node
-		Cursor_node = node
-		edit.mouse_press(node.editor, x,y, mouse_button)
-		return
+	if Global_state.root then
+		mouse_press_on_surface(x,y, mouse_button)
 	end
-	-- pan surface
-	Pan = {x=Viewport.x+x/Viewport.zoom,y=Viewport.y+y/Viewport.zoom}
 end
\ No newline at end of file
diff --git a/0012-on.initialize b/0012-on.initialize
index c548742..c40a24a 100644
--- a/0012-on.initialize
+++ b/0012-on.initialize
@@ -1,4 +1,11 @@
 on.initialize = function()
+	Files = love.filesystem.getDirectoryItems('data')
+	for i=#Files,1,-1 do
+		if (not Files[i]:match('%.md$')) or Files[i]:match('%-%d+.md$') then
+			table.remove(Files, i)
+		end
+	end
+	table.sort(Files)
 	new_definition()
 	A()
 end
\ No newline at end of file
diff --git a/0023-on.keychord_press b/0023-on.keychord_press
index 043d404..ab19d95 100644
--- a/0023-on.keychord_press
+++ b/0023-on.keychord_press
@@ -14,8 +14,6 @@ on.keychord_press = function(chord, key)
 		-- reset zoom
 		Viewport.zoom = 1.0
 		B()
-	elseif chord == 'C-q' then
-		live.send_to_app('QUIT')
 	elseif Cursor_node then
 		local old_top = {line=Cursor_node.editor.screen_top1.line, pos=Cursor_node.editor.screen_top1.pos}
 		edit.keychord_press(Cursor_node.editor, chord, key)
diff --git a/0026-on.draw b/0026-on.draw
index ddc390d..4590425 100644
--- a/0026-on.draw
+++ b/0026-on.draw
@@ -1,25 +1,11 @@
 on.draw = function()
-	for _,obj in ipairs(Surface) do
-		love.graphics.setColor(obj.r or 0, obj.g or 0, obj.b or 0)
-		if obj.type == 'rectangle' then
-			love.graphics.rectangle(obj.drawmode or 'fill', vx(obj.x),vy(obj.y), scale(obj.w),scale(obj.h), scale(obj.rx or 5), scale(obj.ry or 5))
-		elseif obj.type == 'line' then
-			love.graphics.line(unpack(obj.zdata))
-		elseif obj.type == 'circle' then
-			love.graphics.circle(obj.drawmode or 'fill', vx(obj.x), vy(obj.y), scale(obj.radius))
-		elseif obj.type == 'arc' then
-			love.graphics.arc(obj.drawmode or 'line', obj.arctype or 'open', vx(obj.x), vy(obj.y), scale(obj.radius), obj.angle1, obj.angle2, obj.segments)
-		elseif obj.type == 'ellipse' then
-			love.graphics.ellipse(obj.drawmode or 'fill', vx(obj.x), vy(obj.y), scale(obj.radiusx), scale(obj.radiusy))
-		elseif obj.type == 'bezier' then
-			love.graphics.line(unpack(obj.zdata))
-		elseif obj.type == 'text' then
-			if obj.w == nil then
-				love.graphics.draw(obj.text, vx(obj.x), vy(obj.y))
-			else
-				edit.draw(obj.editor, obj.fg, not obj.show_cursor)
-			end
-		end
+	Global_state.button_handlers = {}
+	local font = love.graphics.getFont()
+	font:setLineHeight(1.3)
+	if Global_state.root == nil then
+		-- TODO: use surface for file picker as well
+		draw_file_picker()
+	else
+		draw_surface()
 	end
-	draw_menu_bar()
 end
\ No newline at end of file
diff --git a/0081-draw_menu_bar b/0081-draw_menu_bar
index 43d5225..e7d0720 100644
--- a/0081-draw_menu_bar
+++ b/0081-draw_menu_bar
@@ -6,6 +6,7 @@ draw_menu_bar = function()
 	love.graphics.rectangle('line', 0,0, App.screen.width, Menu_bar_height)
 	App.color(Menu_command_color)
 	Menu_cursor = 5
+	add_hotkey_to_menu('ctrl+o: switch file')
 	add_hotkey_to_menu('ctrl+f: find')
 	add_hotkey_to_menu('ctrl+left ctrl+right: prev/next word')
 	add_hotkey_to_menu('ctrl+z ctrl+y: undo/redo')
diff --git a/0111-Files b/0111-Files
new file mode 100644
index 0000000..08f64a5
--- /dev/null
+++ b/0111-Files
@@ -0,0 +1 @@
+Files = nil  -- array of filenames
\ No newline at end of file
diff --git a/0112-Global_state b/0112-Global_state
new file mode 100644
index 0000000..4517df5
--- /dev/null
+++ b/0112-Global_state
@@ -0,0 +1,3 @@
+Global_state = {}
+	-- button_handlers: for the file picker
+	-- root: when reading a single thread
\ No newline at end of file
diff --git a/0113-draw_surface b/0113-draw_surface
new file mode 100644
index 0000000..cc003d3
--- /dev/null
+++ b/0113-draw_surface
@@ -0,0 +1,25 @@
+draw_surface = function()
+	for _,obj in ipairs(Surface) do
+		love.graphics.setColor(obj.r or 0, obj.g or 0, obj.b or 0)
+		if obj.type == 'rectangle' then
+			love.graphics.rectangle(obj.drawmode or 'fill', vx(obj.x),vy(obj.y), scale(obj.w),scale(obj.h), scale(obj.rx or 5), scale(obj.ry or 5))
+		elseif obj.type == 'line' then
+			love.graphics.line(unpack(obj.zdata))
+		elseif obj.type == 'circle' then
+			love.graphics.circle(obj.drawmode or 'fill', vx(obj.x), vy(obj.y), scale(obj.radius))
+		elseif obj.type == 'arc' then
+			love.graphics.arc(obj.drawmode or 'line', obj.arctype or 'open', vx(obj.x), vy(obj.y), scale(obj.radius), obj.angle1, obj.angle2, obj.segments)
+		elseif obj.type == 'ellipse' then
+			love.graphics.ellipse(obj.drawmode or 'fill', vx(obj.x), vy(obj.y), scale(obj.radiusx), scale(obj.radiusy))
+		elseif obj.type == 'bezier' then
+			love.graphics.line(unpack(obj.zdata))
+		elseif obj.type == 'text' then
+			if obj.w == nil then
+				love.graphics.draw(obj.text, vx(obj.x), vy(obj.y))
+			else
+				edit.draw(obj.editor, obj.fg, not obj.show_cursor)
+			end
+		end
+	end
+	draw_menu_bar()
+end
\ No newline at end of file
diff --git a/0114-draw_file_picker b/0114-draw_file_picker
new file mode 100644
index 0000000..5637aa6
--- /dev/null
+++ b/0114-draw_file_picker
@@ -0,0 +1,25 @@
+draw_file_picker = function()
+	local font = love.graphics.getFont()
+	local y, x = Margin_top, Margin_left
+	for _,f in ipairs(Files) do
+		local w = font:getWidth(f)
+		if x + w > App.screen.width then
+			y = y + font:getHeight()*font:getLineHeight() + 10
+			x = Margin_left
+		end
+		button(Global_state, f, {
+			x=x-5, y=y-2, w=w+10, h=font:getHeight()*font:getLineHeight()+4,
+			color={0.7,0.7,1.0},
+			icon=function(p)
+				App.color{r=0.4,g=0.4,b=0.7}
+				love.graphics.rectangle('line', p.x,p.y, p.w,p.h, 5,5)
+				App.color{r=0,g=0,b=0}
+				love.graphics.print(f, x,y)
+			end,
+			onpress1 = function()
+				open_thread(f)
+			end,
+		})
+		x = x + App.width(f) + 15
+	end
+end
\ No newline at end of file
diff --git a/0115-update_font_size b/0115-update_font_size
new file mode 100644
index 0000000..6bed895
--- /dev/null
+++ b/0115-update_font_size
@@ -0,0 +1,11 @@
+update_font_size = function(n)
+	Font_height = n
+	love.graphics.setFont(love.graphics.newFont(Font_height))
+	local font = love.graphics.getFont()
+	font:setLineHeight(1.3)
+	Line_height = math.floor(Font_height*1.3)
+	Menu_bar_height = 5 + Line_height + 5
+	if Global_state.root then
+		edit.update_font_settings(Global_state, n)
+	end
+end
diff --git a/0116-mouse_press_on_surface b/0116-mouse_press_on_surface
new file mode 100644
index 0000000..1b1690d
--- /dev/null
+++ b/0116-mouse_press_on_surface
@@ -0,0 +1,18 @@
+mouse_press_on_surface = function(x,y, mouse_button)
+	if Cursor_node then
+		Cursor_node.show_cursor = nil
+		Cursor_node = nil
+	end
+	if mouse_press_consumed_by_any_button_handler(HUD, x,y, mouse_button) then
+		return
+	end
+	local node = on_text(x,y)
+	if node then
+		-- position cursor in node
+		Cursor_node = node
+		edit.mouse_press(node.editor, x,y, mouse_button)
+		return
+	end
+	-- pan surface
+	Pan = {x=Viewport.x+x/Viewport.zoom,y=Viewport.y+y/Viewport.zoom}
+end
\ No newline at end of file
diff --git a/0117-open_thread b/0117-open_thread
new file mode 100644
index 0000000..9ac8a0e
--- /dev/null
+++ b/0117-open_thread
@@ -0,0 +1,9 @@
+open_thread = function(filename)
+	local font = love.graphics.getFont()
+	local em_width = font:getWidth('m')
+	Global_state.root = load_subtree(filename, Margin_left, em_width)
+	Global_state.root.top = Menu_bar_height + Margin_top
+	-- HERE: Cursor_node needs to be set at the Surface level of abstraction
+	--Cursor_node = Global_state.root
+	love.window.setTitle('pothi.love - '..Global_state.root.id)
+end
\ No newline at end of file
diff --git a/0118-load_subtree b/0118-load_subtree
new file mode 100644
index 0000000..116916a
--- /dev/null
+++ b/0118-load_subtree
@@ -0,0 +1,11 @@
+load_subtree = function(filename, left, em_width)
+	-- load a file and recursively all replies to it
+--	print('load_subtree', filename)
+	local state = initialize_item(0, left, left+40*em_width, filename)
+	local replies = load_metadata(filename).replies
+	for i,reply_id in ipairs(replies) do
+		local reply = load_subtree(reply_id, left+2*em_width, em_width)
+		table.insert(state.replies, reply)
+	end
+	return state
+end
\ No newline at end of file
diff --git a/0119-load_metadata b/0119-load_metadata
new file mode 100644
index 0000000..f3de79c
--- /dev/null
+++ b/0119-load_metadata
@@ -0,0 +1,8 @@
+load_metadata = function(filename)
+	local mfile = metadata_file(filename)
+	local mpath = save_dir_path(mfile)
+	if not love.filesystem.getInfo(mpath) then
+		return {replies={}}
+	end
+	return json.decode(love.filesystem.read(mpath))
+end
\ No newline at end of file
diff --git a/0120-initialize_item b/0120-initialize_item
new file mode 100644
index 0000000..d3b391e
--- /dev/null
+++ b/0120-initialize_item
@@ -0,0 +1,11 @@
+initialize_item = function(top, left, right, filename)
+	local font = love.graphics.getFont()
+	local result = edit.initialize_state(top, left, right, font:getHeight(), font:getHeight()*font:getLineHeight())
+	result.id = filename
+	result.filename = full_path(filename)
+	result.editable = false
+	result.replies = {}
+	load_from_disk(result)
+	Text.redraw_all(result)
+	return result
+end
\ No newline at end of file
diff --git a/0121-full_path b/0121-full_path
new file mode 100644
index 0000000..67b0f56
--- /dev/null
+++ b/0121-full_path
@@ -0,0 +1,3 @@
+full_path = function(id)
+	return  love.filesystem.getSaveDirectory()..'/data/'..id
+end
\ No newline at end of file
diff --git a/0122-metadata_file b/0122-metadata_file
new file mode 100644
index 0000000..f146acd
--- /dev/null
+++ b/0122-metadata_file
@@ -0,0 +1,3 @@
+metadata_file = function(filename)
+	return  filename:gsub('%.md$', '')..'.json'
+end
\ No newline at end of file
diff --git a/0123-save_dir_path b/0123-save_dir_path
new file mode 100644
index 0000000..b958190
--- /dev/null
+++ b/0123-save_dir_path
@@ -0,0 +1,3 @@
+save_dir_path = function(id)
+	return 'data/'..id
+end
\ No newline at end of file