diff --git a/2017/01.cpp b/2017/01.cpp
index 459b6ae..751683e 100644
--- a/2017/01.cpp
+++ b/2017/01.cpp
@@ -46,9 +46,10 @@ TEST_SUITE("2017-01 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string input;
-  std::getline(*aocpp::Startup(argc, argv), input);
+  std::getline(in, input);
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
 }
diff --git a/2017/02.cpp b/2017/02.cpp
index b97c263..fbf78f7 100644
--- a/2017/02.cpp
+++ b/2017/02.cpp
@@ -66,10 +66,9 @@ TEST_SUITE("2017-02 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto in_ptr = aocpp::Startup(argc, argv);
-  auto & in = *in_ptr;
-  auto [p1,p2] = Omnibus(in);
+auto Main(std::istream & in) -> void
+{
+  auto const [p1,p2] = Omnibus(in);
   std::cout << "Part 1: " << p1 << std::endl;
   std::cout << "Part 2: " << p2 << std::endl;
 }
diff --git a/2017/05.cpp b/2017/05.cpp
index be2b288..5ae5b11 100644
--- a/2017/05.cpp
+++ b/2017/05.cpp
@@ -57,8 +57,9 @@ TEST_SUITE("2017-05 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto input {Parse(in)};
   std::cout << "Part 1: " << Run1(input) << std::endl;
   std::cout << "Part 2: " << Run2(std::move(input)) << std::endl;
 }
diff --git a/2017/06.cpp b/2017/06.cpp
index f4db489..2531b61 100644
--- a/2017/06.cpp
+++ b/2017/06.cpp
@@ -80,9 +80,10 @@ TEST_SUITE("2017-06 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*aocpp::Startup(argc, argv));
-  auto answer = CycleSearch(input);
+auto Main(std::istream & in) -> void
+{
+  auto input {Parse(in)};
+  auto const answer = CycleSearch(input);
   std::cout << "Part 1: " << answer.first << std::endl;
   std::cout << "Part 2: " << answer.second << std::endl;
 }
diff --git a/2017/10.cpp b/2017/10.cpp
index ed22575..716c9ec 100644
--- a/2017/10.cpp
+++ b/2017/10.cpp
@@ -9,9 +9,10 @@
 #include <aocpp/Parsing.hpp>
 #include <knothash.hpp>
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string line;
-  std::getline(*aocpp::Startup(argc, argv), line);
+  std::getline(in, line);
 
   std::vector<std::uint8_t> lengths1;
   for (auto && x : aocpp::SplitOn(line, ",")) {
@@ -22,4 +23,4 @@ auto main(int argc, char** argv) -> int {
   std::cout << "Part 1: " << long{result[0]} * long{result[1]} << std::endl;
 
   std::cout << "Part 2: " << knothash::render(knothash::hash(line)) << std::endl;
-}
\ No newline at end of file
+}
diff --git a/2017/11.cpp b/2017/11.cpp
index d879964..52add10 100644
--- a/2017/11.cpp
+++ b/2017/11.cpp
@@ -60,10 +60,11 @@ TEST_SUITE("2017-11 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string line;
-  std::getline(*Startup(argc, argv), line);
-  auto [part1, part2] = Walk(line);
+  std::getline(in, line);
+  auto const [part1, part2] = Walk(line);
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << part2 << std::endl;
-}
\ No newline at end of file
+}
diff --git a/2017/12.cpp b/2017/12.cpp
index 54c83ef..71206c6 100644
--- a/2017/12.cpp
+++ b/2017/12.cpp
@@ -101,9 +101,10 @@ TEST_SUITE("2017-12 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*Startup(argc, argv));
-  auto [part1, part2] = LinkNodes(input);
+auto Main(std::istream & in) -> void
+{
+  auto const input {Parse(in)};
+  auto const [part1, part2] = LinkNodes(input);
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << part2 << std::endl;
-}
\ No newline at end of file
+}
diff --git a/2017/13.cpp b/2017/13.cpp
index 682d578..8db6965 100644
--- a/2017/13.cpp
+++ b/2017/13.cpp
@@ -40,7 +40,7 @@ auto Caught(std::vector<Scanner> const& scanners) -> std::size_t {
   return severity;
 }
 
-auto Delay(std::vector<Scanner> & scanners) {
+auto Delay(std::vector<Scanner> scanners) {
   std::uint64_t delay = 0;
 
   for (;;) {
@@ -72,8 +72,9 @@ TEST_SUITE("2017-12 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto input {Parse(in)};
   std::cout << "Part 1: " << Caught(input) << std::endl;
-  std::cout << "Part 2: " << Delay(input) << std::endl;
-}
\ No newline at end of file
+  std::cout << "Part 2: " << Delay(std::move(input)) << std::endl;
+}
diff --git a/2017/14.cpp b/2017/14.cpp
index 4418943..847d4ee 100644
--- a/2017/14.cpp
+++ b/2017/14.cpp
@@ -94,10 +94,11 @@ TEST_CASE("flqrgnkx") {
 }
 }
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string input;
-  std::getline(*aocpp::Startup(argc, argv), input);
-  auto rows = MakeRows(std::move(input));
+  std::getline(in, input);
+  auto const rows {MakeRows(std::move(input))};
   std::cout << "Part 1: " << CountBits(rows) << std::endl;
   std::cout << "Part 2: " << CountComponents(rows) << std::endl;
-}
\ No newline at end of file
+}
diff --git a/2017/17.cpp b/2017/17.cpp
index bab4834..ce42cbf 100644
--- a/2017/17.cpp
+++ b/2017/17.cpp
@@ -59,9 +59,10 @@ TEST_SUITE("2017-17 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   int steps;
-  *Startup(argc, argv) >> steps;
+  in >> steps;
   std::cout << "Part 1: " << Part1(steps, 2017) << std::endl;
   std::cout << "Part 2: " << Part2(steps, 50'000'000) << std::endl;
-}
\ No newline at end of file
+}
diff --git a/2017/18.cpp b/2017/18.cpp
index fa35066..7f92e4f 100644
--- a/2017/18.cpp
+++ b/2017/18.cpp
@@ -237,8 +237,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const program = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const program {Parse(in)};
   std::cout << "Part 1: " << Part1(program) << std::endl;
   std::cout << "Part 2: " << Part2(program) << std::endl;
 }
diff --git a/2017/19.cpp b/2017/19.cpp
index 1725a60..9e61eab 100644
--- a/2017/19.cpp
+++ b/2017/19.cpp
@@ -65,15 +65,15 @@ TEST_SUITE("2017-19 examples") {
       "     +B-+  +--+ \n"
       "                \n"
     };
-    auto [p1,p2] = Drive(Grid::Parse(in));
+    auto const [p1, p2] = Drive(Grid::Parse(in));
     CHECK(p1 == "ABCDEF");
     CHECK(p2 == 38);
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Grid::Parse(*aocpp::Startup(argc, argv));
-  auto [part1, part2] = Drive(input);
+auto Main(std::istream & in) -> void
+{
+  auto const [part1, part2] = Drive(Grid::Parse(in));
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << part2 << std::endl;
 }
diff --git a/2018/15.cpp b/2018/15.cpp
index 5cd2430..c6f8c1f 100644
--- a/2018/15.cpp
+++ b/2018/15.cpp
@@ -476,8 +476,9 @@ TEST_SUITE("2018-15 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto grid = Grid::Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const grid {Grid::Parse(in)};
   Game game {std::move(grid)};
   //game.debug_out_ = &std::cout;
   std::cout << "Part 1: " << *Game{game}.Simulate() << std::endl;
diff --git a/2019/01.cpp b/2019/01.cpp
index 75a33f8..ddcb2f4 100644
--- a/2019/01.cpp
+++ b/2019/01.cpp
@@ -44,10 +44,8 @@ TEST_CASE("part 2") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto in_ptr = aocpp::Startup(argc, argv);
-  auto & in = *in_ptr;
-
+auto Main(std::istream & in) -> void
+{
   std::int64_t weight;
   std::int64_t part1 = 0;
   std::int64_t part2 = 0;
diff --git a/2019/02.cpp b/2019/02.cpp
index 14770f6..0e4221f 100644
--- a/2019/02.cpp
+++ b/2019/02.cpp
@@ -36,8 +36,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
 
   std::cout << "Part 1: " << Compute(machine, 12, 2) << std::endl;
 
diff --git a/2019/03.cpp b/2019/03.cpp
index ae8ffe5..2d66fb2 100644
--- a/2019/03.cpp
+++ b/2019/03.cpp
@@ -66,10 +66,8 @@ auto Record (
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto in_ptr = aocpp::Startup(argc, argv);
-  auto & in = *in_ptr;
-
+auto Main(std::istream & in) -> void
+{
   std::string line;
   std::getline(in, line);
   auto wire0 = BuildLine(line);
diff --git a/2019/04.cpp b/2019/04.cpp
index d6ade1a..220e642 100644
--- a/2019/04.cpp
+++ b/2019/04.cpp
@@ -43,8 +43,9 @@ auto Valid2(std::string const& str) {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto [lo,hi] = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const [lo,hi] = Parse(in);
 
   std::int64_t part1 = 0;
   std::int64_t part2 = 0;
diff --git a/2019/05.cpp b/2019/05.cpp
index 62f9b40..982f775 100644
--- a/2019/05.cpp
+++ b/2019/05.cpp
@@ -17,8 +17,9 @@ auto Compute(Machine machine, ValueType d) -> ValueType {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
   std::cout << "Part 1: " << Compute(machine, 1) << std::endl;
   std::cout << "Part 2: " << Compute(std::move(machine), 5) << std::endl;
 }
diff --git a/2019/06.cpp b/2019/06.cpp
index 0830e11..1b4c0b6 100644
--- a/2019/06.cpp
+++ b/2019/06.cpp
@@ -88,8 +88,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto parents = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const parents {Parse(in)};
   std::cout << "Part 1: " << Part1(parents) << std::endl;
   std::cout << "Part 2: " << Part2(parents) << std::endl;
 }
diff --git a/2019/07.cpp b/2019/07.cpp
index 1b5182d..8f9d5d7 100644
--- a/2019/07.cpp
+++ b/2019/07.cpp
@@ -85,8 +85,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
   std::cout << "Part 1: " << Part1(machine) << std::endl;
   std::cout << "Part 2: " << Part2(std::move(machine)) << std::endl;
 }
diff --git a/2019/08.cpp b/2019/08.cpp
index 4a8974d..c8dda9e 100644
--- a/2019/08.cpp
+++ b/2019/08.cpp
@@ -56,9 +56,10 @@ auto Draw(std::string const& picture) {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string line;
-  std::getline(*aocpp::Startup(argc, argv), line);
+  std::getline(in, line);
   std::cout << "Part 1: " << Part1(line) << std::endl;
   Draw(Flatten(line));
 }
diff --git a/2019/09.cpp b/2019/09.cpp
index 96c7dcc..c9520f9 100644
--- a/2019/09.cpp
+++ b/2019/09.cpp
@@ -29,8 +29,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
   std::cout << "Part 1: " << Compute(machine, 1) << std::endl;
   std::cout << "Part 2: " << Compute(std::move(machine), 2) << std::endl;
 }
diff --git a/2019/10.cpp b/2019/10.cpp
index 0ca9e25..007a04d 100644
--- a/2019/10.cpp
+++ b/2019/10.cpp
@@ -208,9 +208,10 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto grid = Grid::Parse(*Startup(argc, argv));
-  auto [part1, base] = Part1(grid);
+auto Main(std::istream & in) -> void
+{
+  auto const grid {Grid::Parse(in)};
+  auto const [part1, base] = Part1(grid);
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << Part2(grid, base, 200) << std::endl;
 }
diff --git a/2019/11.cpp b/2019/11.cpp
index 5b8740b..fe948fe 100644
--- a/2019/11.cpp
+++ b/2019/11.cpp
@@ -37,8 +37,9 @@ auto Compute(Machine machine, ValueType start)
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
   std::cout << "Part 1: " << Compute(machine, 0).size() << "\nPart 2\n";
   Draw(std::cout, Compute(std::move(machine), 1));
 }
diff --git a/2019/12.cpp b/2019/12.cpp
index 685c832..5df8a95 100644
--- a/2019/12.cpp
+++ b/2019/12.cpp
@@ -93,10 +93,11 @@ auto Part2(std::array<std::vector<Particle>, 3> const& ps) {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto ps = Parse(*aocpp::Startup(argc, argv));
-  auto part2 = Part2(ps);
-  auto part1 = Part1(std::move(ps), 1000);
+auto Main(std::istream & in) -> void
+{
+  auto ps = Parse(in);
+  auto const part2 = Part2(ps);
+  auto const part1 = Part1(std::move(ps), 1000);
 
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << part2 << std::endl;
diff --git a/2019/13.cpp b/2019/13.cpp
index 2a3a5b9..03de0fd 100644
--- a/2019/13.cpp
+++ b/2019/13.cpp
@@ -59,8 +59,9 @@ auto Compute2(Machine machine) {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
   std::cout << "Part 1: " << Compute1(machine) << std::endl;
   std::cout << "Part 2: " << Compute2(std::move(machine)) << std::endl;
 }
diff --git a/2019/14.cpp b/2019/14.cpp
index ac450f0..cf5640c 100644
--- a/2019/14.cpp
+++ b/2019/14.cpp
@@ -228,11 +228,12 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto recipes = Parse(*aocpp::Startup(argc, argv));
-  auto machine = Machine(recipes);
-  auto part1 = machine(1);
-  auto part2 = ComputeFuel(machine, 1'000'000'000'000);
+auto Main(std::istream & in) -> void
+{
+  auto const recipes {Parse(in)};
+  auto machine {Machine(recipes)};
+  auto const part1 {machine(1)};
+  auto const part2 {ComputeFuel(machine, 1'000'000'000'000)};
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << part2 << std::endl;
 }
diff --git a/2019/15.cpp b/2019/15.cpp
index d4a3b63..5c5929c 100644
--- a/2019/15.cpp
+++ b/2019/15.cpp
@@ -92,8 +92,9 @@ auto Compute(std::map<Coord, ValueType> world) -> std::pair<int, int> {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto [p1,p2] = Compute(Explore(Machine{ParseStream(*aocpp::Startup(argc, argv))}));
+auto Main(std::istream & in) -> void
+{
+  auto const [p1,p2] = Compute(Explore(Machine{ParseStream(in)}));
   std::cout << "Part 1: " << p1 << std::endl;
   std::cout << "Part 2: " << p2 << std::endl;
 }
diff --git a/2019/16.cpp b/2019/16.cpp
index 61e3c6a..397124c 100644
--- a/2019/16.cpp
+++ b/2019/16.cpp
@@ -118,8 +118,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const input = Parse(in);
 
   std::cout << "Part 1: " << Compute(input, 100, 0) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
diff --git a/2019/17.cpp b/2019/17.cpp
index 5a45333..fc14455 100644
--- a/2019/17.cpp
+++ b/2019/17.cpp
@@ -213,14 +213,15 @@ auto GatherScore(Machine m, std::string const& program) -> ValueType {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto machine = Machine{ParseStream(*aocpp::Startup(argc, argv))};
-  auto grid = GatherOutput(machine);
-  auto part1 = ScaffoldAlignments(grid);
-  auto path = ComputePath(grid);
-  auto program = ComputeProgram(path);
+auto Main(std::istream & in) -> void
+{
+  auto machine = Machine{ParseStream(in)};
+  auto const grid = GatherOutput(machine);
+  auto const part1 = ScaffoldAlignments(grid);
+  auto const path = ComputePath(grid);
+  auto const program = ComputeProgram(path);
   std::cout << "Part 1: " << part1 << std::endl;
   
-  auto part2 = GatherScore(std::move(machine), program);
+  auto const part2 = GatherScore(std::move(machine), program);
   std::cout << "Part 2: " << part2 << std::endl;
 }
diff --git a/2019/18.cpp b/2019/18.cpp
index c2dcf86..0a62af0 100644
--- a/2019/18.cpp
+++ b/2019/18.cpp
@@ -160,8 +160,9 @@ auto Part2(Grid & grid, Features & features) {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto grid = Grid::Parse(*Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto grid = Grid::Parse(in);
   auto features = FindFeatures(grid);
   auto distances = FindDistances(grid, features);
   std::cout << "Part 1: " << SolveMaze(distances, "@") << std::endl;
diff --git a/2019/19.cpp b/2019/19.cpp
index b5e8f0f..a9a6b8c 100644
--- a/2019/19.cpp
+++ b/2019/19.cpp
@@ -45,8 +45,9 @@ auto Part2(Scanner const& scanner) {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto scanner = Scanner{Machine{ParseStream(*aocpp::Startup(argc, argv))}};
+auto Main(std::istream & in) -> void
+{
+  auto const scanner = Scanner{Machine{ParseStream(in)}};
   std::cout << "Part 1: " << Part1(scanner) << std::endl;
   std::cout << "Part 2: " << Part2(scanner) << std::endl;
 }
diff --git a/2019/20.cpp b/2019/20.cpp
index a1d33d3..ed64530 100644
--- a/2019/20.cpp
+++ b/2019/20.cpp
@@ -275,10 +275,11 @@ TEST_SUITE("2019-20 examples") {
 }
 
 
-auto main(int argc, char** argv) -> int {
-  auto map = Grid::Parse(*Startup(argc, argv));
-  auto portals = FindPortals(map);
-  auto distances = FindDistances(map, portals);
+auto Main(std::istream & in) -> void
+{
+  auto const map {Grid::Parse(in)};
+  auto const portals {FindPortals(map)};
+  auto const distances {FindDistances(map, portals)};
 
   std::cout << "Part 1: " << SolveMaze(distances, false) << std::endl;
   std::cout << "Part 2: " << SolveMaze(distances, true) << std::endl;
diff --git a/2019/21.cpp b/2019/21.cpp
index af00136..a52c5e9 100644
--- a/2019/21.cpp
+++ b/2019/21.cpp
@@ -262,8 +262,9 @@ auto Compute(
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  Machine machine {ParseStream(*aocpp::Startup(argc, argv))};
+auto Main(std::istream & in) -> void
+{
+  Machine machine {ParseStream(in)};
 
   Compute(machine, 4,
   { "#####.###########",
diff --git a/2019/22.cpp b/2019/22.cpp
index f0a1f94..e680250 100644
--- a/2019/22.cpp
+++ b/2019/22.cpp
@@ -114,13 +114,15 @@ auto Many(Shuffle<Cards> shuffle, unsigned long n) -> Shuffle<Cards> {
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
-  auto instructions = Parse(*Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const instructions {Parse(in)};
 
-  auto shuffle1 = FollowInstructions<10007>(instructions);
+  auto const shuffle1 {FollowInstructions<10007>(instructions)};
   std::cout << "Part 1: " << shuffle1(2019) << std::endl;
 
-  auto shuffle2 = FollowInstructions<119315717514047>(instructions);
+  auto shuffle2 {FollowInstructions<119315717514047>(instructions)};
   shuffle2 = Many(shuffle2, 101741582076661);
-  std::cout << "Part 2: " << shuffle2.inverse()(2020) << std::endl;
+  shuffle2 = shuffle2.inverse();
+  std::cout << "Part 2: " << shuffle2(2020) << std::endl;
 }
diff --git a/2019/23.cpp b/2019/23.cpp
index e4e272d..9b90ea6 100644
--- a/2019/23.cpp
+++ b/2019/23.cpp
@@ -55,8 +55,9 @@ auto Interact(Ethernet & ethernet, Machine & m, std::optional<Payload> p) -> voi
 
 } // namespace
 
-auto main(int const argc, char** const argv) -> int {
-  auto machines = BuildNetwork(Machine{ParseStream(*aocpp::Startup(argc, argv))});
+auto Main(std::istream & in) -> void
+{
+  auto machines = BuildNetwork(Machine{ParseStream(in)});
   auto ethernet = Ethernet{};
 
   std::optional<ValueType> part1;
diff --git a/2019/24.cpp b/2019/24.cpp
index 70156cb..f20aedc 100644
--- a/2019/24.cpp
+++ b/2019/24.cpp
@@ -135,8 +135,9 @@ TEST_SUITE("documented examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const bugs = FindBugs(Grid::Parse(*Startup(argc, argv)));
+auto Main(std::istream & in) -> void
+{
+  auto const bugs {FindBugs(Grid::Parse(in))};
   std::cout << "Part 1: " << Part1(bugs) << std::endl;
   std::cout << "Part 2: " << Part2(std::move(bugs), 200) << std::endl;
 }
diff --git a/2019/25.cpp b/2019/25.cpp
index e18cacd..06c2ccf 100644
--- a/2019/25.cpp
+++ b/2019/25.cpp
@@ -58,7 +58,8 @@ auto Search(std::string & script)
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string script =
   "north\n" "take sand\n"
   "north\n" "take space heater\n"
@@ -76,5 +77,5 @@ auto main(int argc, char** argv) -> int {
 
   Search(script);
 
-  RunWithIO(Machine{ParseStream(*aocpp::Startup(argc, argv))}, script);
+  RunWithIO(Machine{ParseStream(in)}, script);
 }
diff --git a/2020/01.cpp b/2020/01.cpp
index dfc9dac..92c8d9b 100644
--- a/2020/01.cpp
+++ b/2020/01.cpp
@@ -19,12 +19,12 @@ auto Parse(std::istream & in) -> std::vector<std::int64_t>
   while (in >> x) {
     result.push_back(x);
   }
+  std::sort(result.begin(), result.end());
   return result;
 }
 
-auto Part1(std::vector<std::int64_t> entries) {
+auto Part1(std::vector<std::int64_t> const& entries) {
   std::bitset<2020> numbers;
-  std::sort(entries.begin(), entries.end());
   for (auto const i : entries) {
     if (i >= 2020) {
       break;
@@ -39,9 +39,8 @@ auto Part1(std::vector<std::int64_t> entries) {
   throw std::runtime_error{"no part 1 solution"};
 }
 
-auto Part2(std::vector<std::int64_t> entries) {
+auto Part2(std::vector<std::int64_t> const& entries) {
   std::bitset<2020> numbers;
-  std::sort(entries.begin(), entries.end());
   for (auto const i : entries) {
     if (i >= 2020) { break; }
     if (i < 2020) { numbers.set(i); }
@@ -79,8 +78,9 @@ TEST_CASE("part 2") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto entries = Parse(aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const entries {Parse(in)};
   std::cout << "Part 1: " << Part1(entries) << std::endl;
   std::cout << "Part 2: " << Part2(entries) << std::endl;
 }
diff --git a/2020/02.cpp b/2020/02.cpp
index d25aa90..8ea8c59 100644
--- a/2020/02.cpp
+++ b/2020/02.cpp
@@ -56,10 +56,8 @@ TEST_CASE("part 2") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const in_ptr = aocpp::Startup(argc, argv);
-  auto & in = *in_ptr;
-
+auto Main(std::istream & in) -> void
+{
   std::uint64_t part1{}, part2{};
   
   std::string line;
diff --git a/2020/03.cpp b/2020/03.cpp
index fd4e005..2c943cf 100644
--- a/2020/03.cpp
+++ b/2020/03.cpp
@@ -76,8 +76,9 @@ TEST_CASE("part 2") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto grid = Grid::Parse(*Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const grid {Grid::Parse(in)};
   std::cout << "Part 1: " << Part1(grid) << std::endl;
   std::cout << "Part 2: " << Part2(grid) << std::endl;
 }
diff --git a/2020/10.cpp b/2020/10.cpp
index 05e85f7..fdffed6 100644
--- a/2020/10.cpp
+++ b/2020/10.cpp
@@ -75,8 +75,9 @@ TEST_CASE("part 2") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto adapters = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const adapters {Parse(in)};
   std::cout << "Part 1: " << Part1(adapters) << std::endl;
   std::cout << "Part 2: " << Part2(adapters) << std::endl;
 }
diff --git a/2020/16.cpp b/2020/16.cpp
index 7839184..033024d 100644
--- a/2020/16.cpp
+++ b/2020/16.cpp
@@ -180,12 +180,13 @@ TEST_SUITE("documented examples") {
     };
 
     auto input = Parse(in);
-    REQUIRE(Part1(input) == 71);
+    CHECK(Part1(input) == 71);
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto input {Parse(in)};
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
 }
diff --git a/2020/18.cpp b/2020/18.cpp
index 98b94f2..610bbcc 100644
--- a/2020/18.cpp
+++ b/2020/18.cpp
@@ -140,10 +140,8 @@ TEST_CASE("errors") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const in_ptr = aocpp::Startup(argc, argv);
-  auto & in = *in_ptr;
-
+auto Main(std::istream & in) -> void
+{
   std::int64_t part1 = 0;
   std::int64_t part2 = 0;
   
diff --git a/2020/21.cpp b/2020/21.cpp
index 79edc15..a39e50d 100644
--- a/2020/21.cpp
+++ b/2020/21.cpp
@@ -178,8 +178,9 @@ TEST_CASE("part 2") {
 
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const input = Parse(*Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const input {Parse(in)};
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
 }
diff --git a/2020/CMakeLists.txt b/2020/CMakeLists.txt
index 08cfc13..0d2aa00 100644
--- a/2020/CMakeLists.txt
+++ b/2020/CMakeLists.txt
@@ -1,3 +1,6 @@
+add_executable(2020_01 01.cpp)
+target_link_libraries(2020_01 aocpp)
+
 add_executable(2020_02 02.cpp)
 target_link_libraries(2020_02 aocpp)
 
@@ -14,4 +17,4 @@ add_executable(2020_18 18.cpp)
 target_link_libraries(2020_18 aocpp)
 
 add_executable(2020_21 21.cpp)
-target_link_libraries(2020_21 aocpp dlx)
\ No newline at end of file
+target_link_libraries(2020_21 aocpp dlx)
diff --git a/2022/01.cpp b/2022/01.cpp
index 610d7e8..83db33b 100644
--- a/2022/01.cpp
+++ b/2022/01.cpp
@@ -84,8 +84,9 @@ TEST_SUITE("2022-01 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const [p1,p2] = Solve(Parse(*aocpp::Startup(argc, argv)));
+auto Main(std::istream & in) -> void
+{
+  auto const [p1,p2] = Solve(Parse(in));
   std::cout << "Part 1: " << p1 << std::endl;
   std::cout << "Part 2: " << p2 << std::endl;
 }
diff --git a/2022/02.cpp b/2022/02.cpp
index 75bc49e..e2ac5a9 100644
--- a/2022/02.cpp
+++ b/2022/02.cpp
@@ -136,8 +136,9 @@ C Z
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto const input {Parse(*aocpp::Startup(argc, argv))} ;
+auto Main(std::istream & in) -> void
+{
+  auto const input {Parse(in)} ;
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
 }
diff --git a/2022/03.cpp b/2022/03.cpp
index 37007a1..8da471c 100644
--- a/2022/03.cpp
+++ b/2022/03.cpp
@@ -97,8 +97,9 @@ TEST_SUITE("2022-03 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto input {Parse(in)};
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
 }
diff --git a/2022/04.cpp b/2022/04.cpp
index 2d93bae..cac7e30 100644
--- a/2022/04.cpp
+++ b/2022/04.cpp
@@ -48,8 +48,9 @@ TEST_SUITE("2022-04 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto [p1,p2] = Solve(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto const [p1,p2] = Solve(in);
   std::cout << "Part 1: " << p1 << std::endl;
   std::cout << "Part 2: " << p2 << std::endl;
 }
diff --git a/2022/06.cpp b/2022/06.cpp
index 1bde1cb..a27d981 100644
--- a/2022/06.cpp
+++ b/2022/06.cpp
@@ -57,9 +57,10 @@ TEST_SUITE("2022-06 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
+auto Main(std::istream & in) -> void
+{
   std::string input;
-  std::getline(*aocpp::Startup(argc, argv), input);
-  std::cout << "Part 1: " << Solve(input, 4) << std::endl;
+  std::getline(in, input);
+  std::cout << "Part 1: " << Solve(input,  4) << std::endl;
   std::cout << "Part 2: " << Solve(input, 14) << std::endl;
 }
diff --git a/2022/08.cpp b/2022/08.cpp
index 941f4d2..b477d2d 100644
--- a/2022/08.cpp
+++ b/2022/08.cpp
@@ -41,8 +41,7 @@ auto Part2(Grid const& grid) -> std::int64_t
   grid.each([&](Coord const c, char const v) {
     auto score = std::transform_reduce(
       std::begin(directions), std::end(directions),
-      std::int64_t{1},
-      std::multiplies(),
+      std::int64_t{1}, std::multiplies(), // product
       [&](Dir const dir) {
         std::int64_t count {0};
         for (auto x = dir(c); grid.contains(x); x = dir(x)) {
@@ -72,9 +71,9 @@ TEST_SUITE("2022-08 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto grid = Grid::Parse(*aocpp::Startup(argc, argv));
+  auto const grid = Grid::Parse(in);
   std::cout << "Part 1: " << Part1(grid) << std::endl;
   std::cout << "Part 2: " << Part2(grid) << std::endl;
 }
diff --git a/2022/09.cpp b/2022/09.cpp
index c044bb5..9d9d058 100644
--- a/2022/09.cpp
+++ b/2022/09.cpp
@@ -97,9 +97,9 @@ TEST_SUITE("2022-09 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto [p1,p2] = Solve(*aocpp::Startup(argc, argv));
+  auto const [p1,p2] = Solve(in);
   std::cout << "Part 1: " << p1 << std::endl;
   std::cout << "Part 2: " << p2 << std::endl;
 }
diff --git a/2022/10.cpp b/2022/10.cpp
index cd105eb..489d75f 100644
--- a/2022/10.cpp
+++ b/2022/10.cpp
@@ -96,9 +96,9 @@ TEST_SUITE("2022-10 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto snapshots = Execute(*aocpp::Startup(argc, argv));
+  auto const snapshots {Execute(in)};
   std::cout << "Part 1: " << Part1(snapshots) << std::endl;
   Part2(snapshots, std::cout << "Part 2:\n");
 }
diff --git a/2022/11.cpp b/2022/11.cpp
index 93bb11e..2c28202 100644
--- a/2022/11.cpp
+++ b/2022/11.cpp
@@ -146,9 +146,9 @@ Monkey 3:
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto const input = Parse(*aocpp::Startup(argc, argv));
+  auto const input {Parse(in)};
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(input) << std::endl;
 }
diff --git a/2022/12.cpp b/2022/12.cpp
index f0d9993..6dde7f0 100644
--- a/2022/12.cpp
+++ b/2022/12.cpp
@@ -84,9 +84,9 @@ TEST_SUITE("2022-12 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto [start, end, grid] = Parse(*aocpp::Startup(argc, argv));
+  auto const [start, end, grid] = Parse(in);
   std::cout << "Part 1: " << Solve({start}, end, grid) << std::endl;
   std::cout << "Part 2: " << Solve(Part2Starts(grid), end, grid) << std::endl;
 }
diff --git a/2022/13.cpp b/2022/13.cpp
index 0ca486c..ae2c1f1 100644
--- a/2022/13.cpp
+++ b/2022/13.cpp
@@ -140,9 +140,9 @@ TEST_SUITE("2022-13 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto input = Parse(*aocpp::Startup(argc, argv));
+  auto input = Parse(in);
   std::cout << "count " << input.size() << std::endl;
   std::cout << "Part 1: " << Part1(input) << std::endl;
   std::cout << "Part 2: " << Part2(std::move(input)) << std::endl;
diff --git a/2022/16.cpp b/2022/16.cpp
index 408a48d..e5e9f97 100644
--- a/2022/16.cpp
+++ b/2022/16.cpp
@@ -332,13 +332,11 @@ Valve JJ has flow rate=21; tunnel leads to valve II
   }
 }
 
-/// @brief Select input source and print solution to part 1 and 2
-/// @param argc Command line argument count
-/// @param argv Command line arguments
-/// @return 0 on success
-auto main(int argc, char** argv) -> int
+/// @brief Print solutions to parts 1 and 2 
+/// @param in selected input stream
+auto Main(std::istream & in) -> void
 {
-  auto rooms = Parse(*aocpp::Startup(argc, argv));
+  auto rooms = Parse(in);
   auto const n = FlowsFirst(rooms);
   auto const [start, distances] = GenerateDistances(rooms);
   rooms.resize(n);
diff --git a/2022/18.cpp b/2022/18.cpp
index ea046c3..3834643 100644
--- a/2022/18.cpp
+++ b/2022/18.cpp
@@ -96,9 +96,9 @@ TEST_SUITE("2022-12 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  auto obj = Parse(*aocpp::Startup(argc, argv));
+  auto const obj {Parse(in)};
   std::cout << "Part 1: " << Part1(obj) << std::endl;
   std::cout << "Part 2: " << Part2(obj) << std::endl;
 }
diff --git a/2022/20.cpp b/2022/20.cpp
index 8c0f635..a004263 100644
--- a/2022/20.cpp
+++ b/2022/20.cpp
@@ -108,8 +108,9 @@ TEST_SUITE("2022-20 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int {
-  auto input = Parse(*aocpp::Startup(argc, argv));
+auto Main(std::istream & in) -> void
+{
+  auto input {Parse(in)};
   std::cout << "Part 1: " << Part1(input) << std::endl;
-  std::cout << "Part 2: " << Part2(input) << std::endl;
+  std::cout << "Part 2: " << Part2(std::move(input)) << std::endl;
 }
diff --git a/2022/25.cpp b/2022/25.cpp
index f508a19..0e7bedc 100644
--- a/2022/25.cpp
+++ b/2022/25.cpp
@@ -87,7 +87,7 @@ TEST_SUITE("2022-25 examples") {
   }
 }
 
-auto main(int argc, char** argv) -> int
+auto Main(std::istream & in) -> void
 {
-  std::cout << "Part 1: " << Solve(*aocpp::Startup(argc, argv)) << std::endl;
+  std::cout << "Part 1: " << Solve(in) << std::endl;
 }
diff --git a/lib/include/aocpp/Startup.hpp b/lib/include/aocpp/Startup.hpp
index fb5208b..d84305c 100644
--- a/lib/include/aocpp/Startup.hpp
+++ b/lib/include/aocpp/Startup.hpp
@@ -17,4 +17,6 @@ auto Startup(int argc, char ** argv) -> std::unique_ptr<std::istream, void(*)(st
 
 }
 
+auto Main(std::istream & in) -> void;
+
 #endif
diff --git a/lib/src/Startup.cpp b/lib/src/Startup.cpp
index 51b9570..590103b 100644
--- a/lib/src/Startup.cpp
+++ b/lib/src/Startup.cpp
@@ -29,3 +29,13 @@ auto Startup(int argc, char ** argv) -> std::unique_ptr<std::istream, void(*)(st
 }
 
 }
+
+auto main(int argc, char ** argv) -> int
+{
+  try {
+    Main(*aocpp::Startup(argc, argv));
+  } catch (std::exception const& e) {
+    std::cerr << "Program failed: " << e.what() << std::endl;
+    return 1;
+  }
+}