diff --git a/0010-on.draw b/0010-on.draw
new file mode 100644
index 0000000..a120a86
--- /dev/null
+++ b/0010-on.draw
@@ -0,0 +1,9 @@
+on.draw = function()
+	if Draw == 'problem' then
+		draw_sum_grid(Problem)
+	elseif Draw == 'char' then
+		draw_sum_grid(Char)
+	else
+		draw_sum_grid(Solution)
+	end
+end
\ No newline at end of file
diff --git a/0011-draw_sum_grid b/0011-draw_sum_grid
new file mode 100644
index 0000000..d15cacc
--- /dev/null
+++ b/0011-draw_sum_grid
@@ -0,0 +1,23 @@
+draw_sum_grid = function(g)
+	-- lines
+	love.graphics.setLineWidth(3)
+	local x1,y1 = 250,200
+	local x2,y2 = 450,400
+	love.graphics.line(x1,y1, x2,y1)
+	love.graphics.line(x1,y2, x2,y2)
+	love.graphics.line(x1,y1, x1,y2)
+	love.graphics.line(x2,y1, x2,y2)
+	local xm,ym = (x1+x2)/2, (y1+y2)/2
+	love.graphics.line(x1,ym, x2,ym)
+	love.graphics.line(xm,y1, xm,y2)
+	-- data
+	draw_cell(g.col_totals[1], x1,y1-Square_side)
+	draw_cell(g.col_totals[2], xm,y1-Square_side)
+	draw_cell(g.row_totals[1], x1-Square_side, y1)
+	draw_cell(g.row_totals[2], x1-Square_side, ym)	
+	for x=1,2 do
+		for y=1,2 do
+			draw_cell(g.data[y][x], x1+(x-1)*Square_side, y1+(y-1)*Square_side)
+		end
+	end
+end
\ No newline at end of file
diff --git a/0012-on.initialize b/0012-on.initialize
new file mode 100644
index 0000000..a6e0a96
--- /dev/null
+++ b/0012-on.initialize
@@ -0,0 +1,5 @@
+on.initialize = function()
+	Font_size = Square_side*0.8
+	Padding = (Square_side-Font_size)/2
+	love.graphics.setFont(love.graphics.newFont(Font_size))
+end
\ No newline at end of file
diff --git a/0013-Square_side b/0013-Square_side
new file mode 100644
index 0000000..4570c08
--- /dev/null
+++ b/0013-Square_side
@@ -0,0 +1 @@
+Square_side = 100
diff --git a/0014-Font_size b/0014-Font_size
new file mode 100644
index 0000000..1e8f84c
--- /dev/null
+++ b/0014-Font_size
@@ -0,0 +1 @@
+Font_size = 0
diff --git a/0015-Padding b/0015-Padding
new file mode 100644
index 0000000..514ea33
--- /dev/null
+++ b/0015-Padding
@@ -0,0 +1 @@
+Padding = 0
\ No newline at end of file
diff --git a/0016-generate_sum_grid b/0016-generate_sum_grid
new file mode 100644
index 0000000..f330c10
--- /dev/null
+++ b/0016-generate_sum_grid
@@ -0,0 +1,14 @@
+generate_sum_grid = function()
+	-- a sum grid is fully characterized by 4 numbers
+	Char = {
+		data = {
+			{ math.random(1,9), math.random(1,9) },
+			{ '', ''},
+		},
+		row_totals = { '', '' },
+	}
+	Char.col_totals = {
+		math.random(Char.data[1][1]+1,10),
+		math.random(Char.data[1][2]+1,10)
+	}
+end
\ No newline at end of file
diff --git a/0017-on.keychord_press b/0017-on.keychord_press
new file mode 100644
index 0000000..0a1b66d
--- /dev/null
+++ b/0017-on.keychord_press
@@ -0,0 +1,14 @@
+on.keychord_press = function(chord, key)
+	if chord == 'C-n' then
+		generate_sum_grid()
+		solve()
+	elseif chord == '`' then
+		if Draw == 'problem' then
+			Draw = 'char'
+		elseif Draw == 'char' then
+			Draw = 'solution'
+		elseif Draw == 'solution' then
+			Draw = 'problem'
+		end
+	end
+end
\ No newline at end of file
diff --git a/0018-Char b/0018-Char
new file mode 100644
index 0000000..a242a72
--- /dev/null
+++ b/0018-Char
@@ -0,0 +1,9 @@
+-- a set of numbers that uniquely characterizes a sum-grid instance.
+Char = {
+	row_totals={0, 0},
+	col_totals={0, 0},
+	data={
+		{0, 0},
+		{0, 0},
+	},
+}
\ No newline at end of file
diff --git a/0019-Solution b/0019-Solution
new file mode 100644
index 0000000..351bf03
--- /dev/null
+++ b/0019-Solution
@@ -0,0 +1,9 @@
+-- solution for the sum-grid problem defined by Char.
+Solution = {
+	row_totals={0, 0},
+	col_totals={0, 0},
+	data={
+		{0, 0},
+		{0, 0},
+	},
+}
\ No newline at end of file
diff --git a/0020-solve b/0020-solve
new file mode 100644
index 0000000..38421ce
--- /dev/null
+++ b/0020-solve
@@ -0,0 +1,21 @@
+solve = function()
+	print('solve')
+	-- copy the slots we have
+	local c = Char.col_totals
+	local d = Char.data
+	Solution = {
+		col_totals = {c[1], c[2]},
+		data = {
+			{d[1][1], d[1][2] },
+			{ },
+		}
+	}
+	-- fill out the remaining data
+	Solution.data[2][1] = c[1] - d[1][1]
+	Solution.data[2][2] = c[2] - d[1][2]
+	d = Solution.data
+	Solution.row_totals = {
+		d[1][1] + d[1][2],
+		d[2][1] + d[2][2],
+	}
+end
\ No newline at end of file
diff --git a/0021-Draw b/0021-Draw
new file mode 100644
index 0000000..6785551
--- /dev/null
+++ b/0021-Draw
@@ -0,0 +1 @@
+Draw = 'char'
\ No newline at end of file
diff --git a/0022-Problem b/0022-Problem
new file mode 100644
index 0000000..0279c88
--- /dev/null
+++ b/0022-Problem
@@ -0,0 +1,8 @@
+Problem = {
+	row_totals={0, 0},
+	col_totals={0, 0},
+	data={
+		{0, 0},
+		{0, 0},
+	},
+}
\ No newline at end of file
diff --git a/0023-draw_cell b/0023-draw_cell
new file mode 100644
index 0000000..652656d
--- /dev/null
+++ b/0023-draw_cell
@@ -0,0 +1,6 @@
+draw_cell = function(n, x,y)
+	local s = tostring(n)
+	local w = App.width(s)
+	local px = (Square_side-w)/2
+	love.graphics.print(s, x+px, y+Padding)
+end
\ No newline at end of file
diff --git a/main.lua b/main.lua
index 1f11c0c..590f432 100644
--- a/main.lua
+++ b/main.lua
@@ -62,9 +62,8 @@ function App.initialize(arg)
 
 
 
-  -- TODO: app-specific stuff goes here
   -- keep a few blank lines around: https://merveilles.town/@akkartik/110084833821965708
-  love.window.setTitle('TODO')
+  love.window.setTitle('Sum Grid')