diff --git a/dub.sdl b/dub.sdl
index eb089b7..c4ec761 100644
--- a/dub.sdl
+++ b/dub.sdl
@@ -3,3 +3,4 @@ description "Advent of Code 2020"
 authors "Chris Josten"
 copyright "Copyright © 2020, Chris Josten"
 license "MIT"
+dependency "fluent-asserts" version="~>0.13.3"
diff --git a/dub.selections.json b/dub.selections.json
new file mode 100644
index 0000000..020f3ff
--- /dev/null
+++ b/dub.selections.json
@@ -0,0 +1,9 @@
+{
+	"fileVersion": 1,
+	"versions": {
+		"ddmp": "0.0.1-0.dev.3",
+		"fluent-asserts": "0.13.3",
+		"libdparse": "0.14.0",
+		"stdx-allocator": "2.77.5"
+	}
+}
diff --git a/in/17.txt b/in/17.txt
new file mode 100644
index 0000000..d8b9ae9
--- /dev/null
+++ b/in/17.txt
@@ -0,0 +1,8 @@
+#......#
+##.#..#.
+#.#.###.
+.##.....
+.##.#...
+##.#....
+#####.#.
+##.#.###
diff --git a/source/app.d b/source/app.d
index fd084cd..d78271d 100644
--- a/source/app.d
+++ b/source/app.d
@@ -24,6 +24,7 @@ import day13;
 import day14;
 import day15;
 import day16;
+import day17;
 import dayutil;
 
 immutable string progName = "aoc-2020";
@@ -49,6 +50,7 @@ Variant function(int, File, bool, string[])[] programs = [
 	&day14.run,
 	&day15.run,
 	&day16.run,
+	&day17.run,
 ];
 
 void printUsage(string message = null) {
diff --git a/source/day17.d b/source/day17.d
new file mode 100644
index 0000000..8cec3de
--- /dev/null
+++ b/source/day17.d
@@ -0,0 +1,102 @@
+import dayutil;
+version(unittest) import fluent.asserts;
+
+struct Point {
+	int x, y, z; 
+
+	int opCmp(ref const Point p) const {
+		return x - p.x + y - p.y + z - p.z;
+	}
+}
+
+Variant run(int part, File input, bool bigboy, string[] args) {
+	bool[Point] parsedInput = parseInput(input.byLine);
+	return Variant(parts!int(part,
+				() => part1(parsedInput)));
+}
+
+bool[Point] parseInput(Range)(Range range) if (isInputRange!Range && isSomeString!(ElementType!Range)){
+	bool[Point] result;
+	foreach(y, line; range.enumerate) {
+		foreach(x, c; line) {
+			if (c == '#') {
+				result[Point(cast(int) x, cast(int) y, 0)] = true;
+			}
+		}
+	}
+	return result;
+}
+
+int part1(bool[Point] start) {
+	immutable int BOOT_LENGTH = 6;
+
+	bool[Point] prev = start.dup;
+	foreach(i; 0..BOOT_LENGTH) {
+		bool[Point] newState = prev.dup;
+		assert(newState == prev);
+
+		int minX, minY, minZ, maxX, maxY, maxZ;
+		foreach(e; prev.byKey) {
+			if (e.x < minX) minX = e.x;
+			if (e.y < minY) minY = e.y;
+			if (e.z < minZ) minZ = e.z;
+			if (e.x > maxX) maxX = e.x;
+			if (e.y > maxY) maxY = e.y;
+			if (e.z > maxZ) maxZ = e.z;
+		}
+		Point min = Point(minX - 1, minY - 1, minZ - 1);
+		Point max = Point(maxX + 2, maxY + 2, maxZ + 2);
+
+		foreach(z; min.z..max.z) {
+			writeln("z=", z);
+			foreach(y; min.y..max.y) {
+				foreach(x; min.x..max.x) {
+					// Point
+					bool active = prev.get(Point(x,y,z), false);
+
+					if (active) { debug write("\x1B[42m"); }
+
+					//write(active ? '#' : '.');
+					int neighboursActive = 0;
+					foreach(dx; x-1..x+2) {
+						foreach(dy; y-1..y+2) {
+							foreach(dz; z-1..z+2) {
+								if (dx == x && dy == y && dz == z) continue;
+								if (prev.get(Point(dx, dy, dz), false)) neighboursActive++;
+							}
+						}
+					}
+					if (neighboursActive > 9) {
+						write("+");
+					} else {
+						write(neighboursActive);
+					}
+
+					if (active && (neighboursActive < 2 || neighboursActive > 3)) {
+						newState[Point(x,y,z)] = false;
+					} else if (!active && neighboursActive == 3) {
+						newState[Point(x,y,z)] = true;
+					}
+					debug write("\x1B[0m");
+				}
+				writeln();
+			}
+			writeln();
+		}
+		assert(newState != prev);
+
+		writeln("---");
+		prev = newState;
+	}
+	return cast(int) prev.byValue.count!((x) => x);
+}
+
+unittest {
+	string[] input = [
+		".#.",
+		"..#",
+		"###"
+	];
+	bool[Point] parsedInput = parseInput(input);
+	part1(parsedInput).should.equal(112);
+}