diff --git a/config b/config
index aa9ac2b..9814436 100644
--- a/config
+++ b/config
@@ -1,2 +1,3 @@
-CONTEST_URL=https://31pwr5t6ij.execute-api.eu-west-2.amazonaws.com
+# CONTEST_URL=https://31pwr5t6ij.execute-api.eu-west-2.amazonaws.com
+CONTEST_URL=http://localhost:8000
 ID="icfp@zeuxis.de DHf1KQyE3vCvMqPaA4LLlw"
diff --git a/server/server.py b/server/server.py
new file mode 100755
index 0000000..acd8c95
--- /dev/null
+++ b/server/server.py
@@ -0,0 +1,299 @@
+#!/usr/bin/env python3
+
+import itertools
+import random
+import subprocess
+from typing import List
+
+import fastapi
+from fastapi.responses import JSONResponse
+from pydantic import BaseModel, Field
+
+api = fastapi.FastAPI()
+
+
+class Problem(BaseModel):
+    rooms: int
+    copies: int
+
+
+PROBLEMS = {
+    "probatio": Problem(rooms=3, copies=1),
+    "primus": Problem(rooms=6, copies=1),
+    "secundus": Problem(rooms=12, copies=1),
+    "tertius": Problem(rooms=18, copies=1),
+    "quartus": Problem(rooms=24, copies=1),
+    "quintus": Problem(rooms=30, copies=1),
+    "aleph": Problem(rooms=6, copies=2),
+    "beth": Problem(rooms=12, copies=2),
+    "gimel": Problem(rooms=18, copies=2),
+    "daleth": Problem(rooms=24, copies=2),
+    "he": Problem(rooms=30, copies=2),
+    "vau": Problem(rooms=6, copies=3),
+    "zain": Problem(rooms=12, copies=3),
+    "hhet": Problem(rooms=18, copies=3),
+    "teth": Problem(rooms=24, copies=3),
+    "iod": Problem(rooms=30, copies=3),
+}
+
+CURRENT_SELECTION = None
+
+
+class Connection(BaseModel):
+    class Port(BaseModel):
+        room: int
+        door: int
+
+    src: Port = Field(alias="from")
+    trg: Port = Field(alias="to")
+
+
+class Map(BaseModel):
+    rooms: List[int]
+    startingRoom: int
+    connections: List[Connection]
+
+
+class Library:
+    class Room:
+        def __init__(self, label):
+            self.label = label
+            self.doors = 6 * [None]
+
+        def __getitem__(self, idx):
+            return self.doors[idx]
+
+        def __setitem__(self, idx, trg):
+            self.doors[idx] = trg
+
+        def __repr__(self):
+            return f"{self.label}: {self.doors}"
+
+    def __init__(self, problem):
+        self.problem = problem
+        self.count = 0
+
+        while True:
+            start = random.randrange(4)
+            self.rooms = [
+                self.Room(lbl) for lbl in itertools.islice(itertools.cycle(range(4)), start, start + problem.rooms)
+            ]
+
+            doors = [(r, d) for r in range(len(self.rooms)) for d in range(6)]
+            while doors:
+                i1 = random.randrange(len(doors))
+                i2 = random.randrange(len(doors))
+                r1, d1 = doors[i1]
+                r2, d2 = doors[i2]
+
+                self.rooms[r1][d1] = r2
+                self.rooms[r2][d2] = r1
+
+                del doors[i1]
+                if i1 < i2:
+                    del doors[i2 - 1]
+                elif i1 > i2:
+                    del doors[i2]
+
+            self.start = 0
+
+            # is connected?
+            visited = set()
+            queue = [self.start]
+            while queue:
+                src = queue.pop(0)
+
+                for d, trg in enumerate(self.rooms[src]):
+                    if self.rooms[src][d] not in visited:
+                        visited.add(trg)
+                        queue.append(self.rooms[src][d])
+
+            if len(visited) != len(self.rooms):
+                continue
+
+            # make copies
+            for c in range(1, problem.copies):
+                for i in range(problem.rooms):
+                    room = self.Room(self.rooms[i].label)
+                    self.rooms.append(room)
+                    for d, trg in enumerate(self.rooms[i].doors):
+                        room[d] = trg + c * problem.rooms
+
+            # connect copies
+            if problem.copies > 1:
+                for _ in range(problem.rooms * problem.copies // 2):
+                    src = random.randrange(problem.rooms)
+                    src_d = random.randrange(6)
+                    cs = list(range(problem.copies))
+                    random.shuffle(cs)
+                    c0 = cs[0] * problem.rooms
+                    c1 = cs[1] * problem.rooms
+
+                    trg = self.rooms[src][src_d] % problem.rooms
+                    trg_d = next(
+                        i for i, t in enumerate(self.rooms[trg].doors) if t % problem.rooms == src % problem.rooms
+                    )
+
+                    self.rooms[c0 + src][src_d] = c1 + trg
+                    self.rooms[c1 + trg][trg_d] = c0 + src
+            break
+
+    def dump(self):
+        for ri, r in enumerate(self.rooms):
+            print(f"   {ri:<2}: {r.label} {r.doors}")
+        print()
+
+    def explore(self, paths: List[str]) -> List[List[int]]:
+        self.count += 1
+
+        results = []
+        for path in paths:
+            pos = self.start
+            marking = False
+            marks = [r.label for r in self.rooms]
+            result = [self.rooms[pos].label]
+
+            for p in path:
+                match p:
+                    case d if "0" <= p < "6":
+                        if marking:
+                            marks[pos] = int(d) % 4
+                        else:
+                            pos = self.rooms[pos][int(d)]
+                        result.append(marks[pos])
+                    case "[":
+                        marking = True
+                    case "]":
+                        marking = False
+                    case _:
+                        pass
+            results.append(result)
+            self.count += 1
+
+        return results
+
+    def guess(self, map):
+        imap = len(self.rooms) * [None]
+        try:
+            assert len(map.rooms) == len(map.rooms), "number of rooms"
+            irooms = [self.Room(lbl) for lbl in map.rooms]
+
+            assert map.startingRoom in range(len(imap)), "starting room is not a room"
+
+            for i, conn in enumerate(map.connections):
+                # print(conn)
+                assert conn.src.room in range(len(imap)), f"{i}.from.room is not a room"
+                assert conn.src.door in range(6), f"{i}.from.room is not a door"
+                assert conn.trg.room in range(len(imap)), f"{i}.to.room is not a room"
+                assert conn.trg.door in range(6), f"{i}.to.room is not a door"
+
+                irooms[conn.src.room][conn.src.door] = conn.trg.room
+                irooms[conn.trg.room][conn.trg.door] = conn.src.room
+
+            for i, r in enumerate(irooms):
+                for d, trg in enumerate(r.doors):
+                    assert trg is not None, f"door {d} of room {i} missing"
+            # self.dump()
+            # for r in irooms:
+            #     print(r)
+
+            queue = [map.startingRoom]
+            imap[map.startingRoom] = self.start
+            visited = set()
+
+            while queue:
+                isrc = queue.pop(0)
+                src = imap[isrc]
+                iroom = irooms[isrc]
+
+                assert iroom.label == self.rooms[src].label, f"wrong label {isrc} {src}"
+                visited.add(isrc)
+
+                for d, itrg in enumerate(iroom.doors):
+                    if imap[itrg] is None:
+                        imap[itrg] = self.rooms[src][d]
+                        queue.append(itrg)
+                    assert imap[itrg] == self.rooms[src][d], f"wrong connection {isrc} {src} [{d}] {itrg} {imap[itrg]}"
+
+            assert len(visited) == len(self.rooms), "not all rooms visited"
+
+        except AssertionError as exc:
+            print(exc)
+            return False
+        return True
+
+
+class Select(BaseModel):
+    id: str
+    problemName: str
+
+    class Problem(BaseModel):
+        problem: str
+        size: int
+        copies: int
+
+    class Response(BaseModel):
+        problemName: str
+
+
+@api.get(path="/select")
+def select_get() -> List[Select.Problem]:
+    return [
+        Select.Problem(problem=pname, size=prob.rooms * prob.copies, copies=prob.copies)
+        for pname, prob in PROBLEMS.items()
+    ]
+    return PROBLEMS
+
+
+@api.post(path="/select")
+def select_post(select: Select) -> Select.Response:
+    global CURRENT_SELECTION
+
+    if select.problemName not in PROBLEMS:
+        return JSONResponse({"detail": "problem not found"}, status_code=404)
+
+    CURRENT_SELECTION = Library(PROBLEMS[select.problemName])
+    CURRENT_SELECTION.dump()
+    return Select.Response(problemName=select.problemName)
+
+
+class Explore(BaseModel):
+    id: str
+    plans: List[str]
+
+    class Response(BaseModel):
+        results: List[List[int]]
+        queryCount: int
+
+
+@api.post(path="/explore")
+def explore(explore: Explore) -> Explore.Response:
+    if not CURRENT_SELECTION:
+        return JSONResponse({"detailno problem selected"}, status_code=409)
+
+    results = CURRENT_SELECTION.explore(explore.plans)
+    return Explore.Response(results=results, queryCount=CURRENT_SELECTION.count)
+
+
+class Guess(BaseModel):
+    id: str
+    map: Map
+
+    class Response(BaseModel):
+        correct: bool
+
+
+@api.post(path="/guess")
+def guess(guess: Guess) -> Guess.Response:
+    global CURRENT_SELECTION
+
+    if not CURRENT_SELECTION:
+        return JSONResponse({"detailno problem selected"}, status_code=409)
+
+    ok = CURRENT_SELECTION.guess(guess.map)
+    CURRENT_SELECTION = None
+    return Guess.Response(correct=ok)
+
+
+if __name__ == "__main__":
+    subprocess.run(["fastapi", "dev", __file__])