diff --git a/aoc2025/Day10.newt b/aoc2025/Day10.newt
new file mode 100644
index 0000000..2c462ae
--- /dev/null
+++ b/aoc2025/Day10.newt
@@ -0,0 +1,126 @@
+module Day10
+
+import Prelude
+import Node
+import Aoc
+import Parser
+import Data.Vect
+import Data.Fin
+import Z3
+
+instance ∀ a b. {{Show a}} → {{Show b}} → Show (Either a b) where
+  show (Left a) = "Left \{show a}"
+  show (Right b) = "Right \{show b}"
+
+record Machine where
+  goal : Int
+  buttons : List Int
+  jolts : List Int
+
+infixr 2 _**_
+
+abs : Int → Int
+abs x = if x < 0 then 0 - x else x
+
+data Σ : (a : U) → (a → U) → U where
+  _**_ : ∀ A. {0 B : A → U} → (x : A) →  (_ : B x) → Σ A B
+
+instance Show Machine where
+  show m  = "Mach{goal=\{show m.goal}, buttons=\{show m.buttons}, goal=\{show m.jolts}}"
+
+parseGroup : Char → Char → Parser (List Int)
+parseGroup start end = do
+  match start
+  nums <- some $ number <* optional (match ',')
+  match end
+  ws
+  pure nums
+
+pfunc pow : Int → Int → Int := `(x,y) => x ** y`
+pfunc xor : Int → Int → Int := `(x,y) => x ^ y`
+
+parseMachine : Parser Machine
+parseMachine = do
+  match '['
+  marks <- some $ match '.' <|> match '#'
+  match ']'
+  ws
+  buttons <- some $ parseGroup '(' ')'
+  costs <- parseGroup '{' '}'
+  pure $ MkMachine (mkgoal marks) (map mkbutton buttons) costs
+  where
+    mkbutton : List Int → Int
+    mkbutton (n :: ns) = pow 2 n + mkbutton ns
+    mkbutton Nil = 0
+
+    mkgoal : List Char → Int
+    mkgoal ('#' :: xs) = 1 + 2 * mkgoal xs
+    mkgoal (_ :: xs) = 2 * mkgoal xs
+    mkgoal Nil = 0
+
+parseFile : Parser (List Machine)
+parseFile = some $ parseMachine <* match '\n'
+
+solve : Machine → Int
+solve m = go 0 m.buttons
+  where
+    go : Int → List Int → Int
+    go st Nil = if st == m.goal then 0 else 999
+    go st (b :: bs) =
+      if st == m.goal
+        then 0
+        else min (1 + go (xor st b) bs) (go st bs)
+
+infixl 7 _&_
+pfunc _&_ : Int → Int → Int := `(x,y) => x & y`
+
+part2z3 : {{Context}} → Machine → Promise Int
+part2z3 {{context}} mach = do
+  let rows = length mach.jolts
+  let (Just todo) = toVect rows mach.jolts | _ => fatalError "jolt/rows length"
+  let vars = map (\i => z3const "x\{show $ fst i}") $ enumerate mach.buttons
+  let solver = newOptimizer context
+
+  traverse_ (constrain solver $ zip vars mach.buttons) (enumerate mach.jolts)
+  for_ vars $ \v => z3add solver $ z3ge v (z3int 0)
+  z3minimize solver $ sum vars
+  "sat" <- z3check solver | res => fatalError "GOT \{res}"
+  model <- getModel solver
+  pure $ foldl _+_ 0 $ map getInt vars
+  where
+    sum : List Arith → Arith
+    sum Nil = z3int 0
+    sum (a :: as) = foldl _+_ a as
+
+    constrain : ∀ b. Solver b → List (Arith × Int) → (Nat × Int) → Promise Unit
+    constrain solver bs (ix, goal) =
+      let mask = pow 2 $ cast ix in
+      z3add solver $ z3eq (z3int goal) $ row mask bs (z3int 0)
+      where
+        row : Int → List (Arith × Int) → Arith → Arith
+        row mask Nil acc = acc
+        row mask ((x , b) :: bs) acc = if b & mask == 0 then row mask bs acc else row mask bs (acc + x)
+
+    button2List : ∀ rows. Vect rows Int → Int → Int → Vect rows Int
+    button2List VNil _ _ = VNil
+    button2List (_ :- rest) mask b =
+      (if (b & mask) == 0 then 0 else 1) :- button2List rest (mask * 2) b
+
+run : String -> Promise Unit
+run fn = do
+  putStrLn {Promise} fn
+  text <- liftIO {Promise} $ readFile fn
+  let (Right (probs,_)) = parseFile (unpack text)
+    | Left msg => putStrLn "ERR: \{msg}"
+  let part1 = foldl _+_ 0 $ map solve probs
+  putStrLn $ "part1 \{show part1}"
+  z3 <- initZ3
+  let context = initContext z3 "main"
+  p2s <- traverse part2z3 probs
+  let p2 = foldl _+_ 0 p2s
+  putStrLn "part2 \{show p2}"
+
+main : IO Unit
+main = runPromise $ do
+  run "aoc2025/day10/eg.txt"
+  run "aoc2025/day10/input.txt"
diff --git a/aoc2025/Node.newt b/aoc2025/Node.newt
index 98bcdb8..dc108a2 100644
--- a/aoc2025/Node.newt
+++ b/aoc2025/Node.newt
@@ -2,6 +2,31 @@ module Node
 
 import Prelude
 
+-- Promise has some sequencing issues with IO
+ptype Promise : U → U
+pfunc promise_bind : ∀ a b. Promise a → (a → Promise b) → Promise b := `(a,b, ma, mab) => ma.then(v => mab(v))`
+pfunc promise_pure : ∀ a. a → Promise a := `(_, a) => Promise.resolve(a)`
+-- The potential issue here is that fa runs before it is even passed in!
+pfunc promise_app : ∀ a b. → Promise (a → b) → Promise a → Promise b := `(a,b,fab,fa) => fab.then(ab => fa.then(a => Promise.resolve(ab(a))))`
+-- This runs everything immediately...
+pfunc promise_lift : ∀ a. IO a → Promise a := `(a,f) => Promise.resolve(f('WORLD').h1)`
+
+instance Monad Promise where
+  bind = promise_bind
+  pure = promise_pure
+
+instance Applicative Promise where
+  return = pure
+  fab <*> fa = promise_app fab fa
+
+instance HasIO Promise where
+  liftIO = promise_lift
+
 pfunc fs : JSObject := `require('fs')`
 pfunc getArgs : List String := `arrayToList(String, process.argv)`
 pfunc readFile uses (MkIORes) : (fn : String) -> IO String := `(fn) => (w) => Prelude_MkIORes(require('fs').readFileSync(fn, 'utf8'), w)`
+
+pfunc runPromise uses (MkIORes MkUnit) : ∀ a. Promise a → IO Unit := `(a,p) => (w) => {
+  // p(w)
+  return Prelude_MkIORes(Prelude_MkUnit, w)
+}`
diff --git a/aoc2025/Z3.newt b/aoc2025/Z3.newt
new file mode 100644
index 0000000..a44b5b9
--- /dev/null
+++ b/aoc2025/Z3.newt
@@ -0,0 +1,46 @@
+module Z3
+
+import Prelude
+import Node
+
+ptype Context
+-- Flag if optimizer or solver
+ptype Solver : Bool → U
+ptype Arith
+ptype Z3Bool
+ptype Model
+ptype Z3
+
+pfunc initZ3 : Promise Z3 := `require('z3-solver').init()`
+pfunc z3ResetMemory : Promise Z3 := `(z3) => z3.Z3.reset_memory()`
+pfunc initContext : Z3 → String → Context := `(z3, name) => z3.Context(name)`
+
+pfunc newSolver : Context → Solver False := `(Context) => new Context.Solver()`
+pfunc newOptimizer : Context → Solver True := `(Context) => new Context.Optimize()`
+
+
+-- These probably should be IO or Promise
+pfunc freshInt : {{Context}} → Promise Arith := `(Context) => Promise.resolve(Context.Int.fresh())`
+pfunc z3const : {{Context}} → String → Arith := `(Context, name) => Context.Int.const(name)`
+pfunc arith_add : Arith → Arith → Arith := `(a,b) => a.add(b)`
+pfunc z3int : {{Context}} → Int → Arith := `(Context,a) => Context.Int.val(a)`
+
+-- We can't overload operators for these because of the return type
+
+pfunc z3eq : Arith → Arith → Z3Bool := `(a,b) => a.eq(b)`
+pfunc z3ge : Arith → Arith → Z3Bool := `(a,b) => a.ge(b)`
+
+pfunc z3add : ∀ b. Solver b → Z3Bool → Promise Unit := `(_, solver, exp) => Promise.resolve(solver.add(exp))`
+pfunc z3minimize : Solver True → Arith → Promise Unit := `(solver, exp) => Promise.resolve(solver.minimize(exp))`
+
+pfunc z3check : ∀ b. Solver b → Promise String := `(b, solver) => solver.check()`
+
+pfunc getModel : ∀ b. Solver b → Promise Model := `(b, solver) => Promise.resolve(solver.model())`
+
+pfunc getInt : {{Model}} → Arith → Int := `(model, exp) => {
+  let n = +(model.eval(exp).toString())
+  return isNaN(n) ? 0 : n
+}`
+
+instance Add Arith where
+  a + b = arith_add a b
diff --git a/aoc2025/Z3Test.newt b/aoc2025/Z3Test.newt
new file mode 100644
index 0000000..ae00b25
--- /dev/null
+++ b/aoc2025/Z3Test.newt
@@ -0,0 +1,38 @@
+module Z3Test
+
+import Prelude
+import Node
+import Z3
+
+test : Promise Unit
+test = do
+  context <- initZ3 "main"
+  x0 <- freshInt
+  x1 <- freshInt
+  x2 <- freshInt
+  x3 <- freshInt
+  x4 <- freshInt
+  x5 <- freshInt
+  let solver = newOptimizer context
+
+  z3add solver $ z3ge x0 $ z3int 0
+  z3add solver $ z3ge x1 $ z3int 0
+  z3add solver $ z3ge x2 $ z3int 0
+  z3add solver $ z3ge x3 $ z3int 0
+  z3add solver $ z3ge x4 $ z3int 0
+  z3add solver $ z3ge x5 $ z3int 0
+
+  z3add solver $ z3eq (x4 + x5) (z3int 3)
+  z3add solver $ z3eq (x1 + x5) (z3int 5)
+  z3add solver $ z3eq (x2 + x3 + x4) (z3int 4)
+  z3add solver $ z3eq (x0 + x1 + x3) (z3int 7)
+
+  z3minimize solver $ x0 + x1 + x2 + x3 + x4 + x5
+
+  res <- z3check solver
+  liftIO $ putStrLn "GOT \{res}"
+
+
+-- switch to promise mode
+main : IO (Promise Unit)
+main = pure test
diff --git a/aoc2025/day10/eg.txt b/aoc2025/day10/eg.txt
new file mode 100644
index 0000000..dd91d7b
--- /dev/null
+++ b/aoc2025/day10/eg.txt
@@ -0,0 +1,3 @@
+[.##.] (3) (1,3) (2) (2,3) (0,2) (0,1) {3,5,4,7}
+[...#.] (0,2,3,4) (2,3) (0,4) (0,1,2) (1,2,3,4) {7,5,12,7,2}
+[.###.#] (0,1,2,3,4) (0,3,4) (0,1,2,4,5) (1,2) {10,11,11,5,10,5}