diff --git a/harald/explore.py b/harald/explore.py
index 68c44b6..71d9874 100755
--- a/harald/explore.py
+++ b/harald/explore.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 
+import itertools
 import functools
 import json
 import os.path
@@ -87,22 +88,24 @@ class Explore:
 
         return path
 
-    def explore(self, path=Path(), probes=None, mark=Path()):
+    def explore(self, paths, probes=None, mark=Path()):
         probes = probes or self.probes
-
-        path = self._path(path)
-        paths = [mark + path + probe for probe in probes]
-
         num_marks = mark.path.count("[")
-        prefix_len = len(mark) - 2 * num_marks + len(path)
+
+        expaths = []
+        for path in paths:
+            path = self._path(path)
+            expaths.extend(mark + path + probe for probe in probes)
 
         print("explore", paths)
-        response = api.explore([p.path for p in paths])
+        response = api.explore([p.path for p in expaths])
         results = response["results"]
         self.score = response["queryCount"]
 
-        print("id", path, results)
-        return [res[prefix_len:] for res in results]
+        for path, presults in zip(paths, itertools.batched(results, len(probes))):
+            prefix_len = len(mark) - 2 * num_marks + len(path)
+            print("id", path, results)
+            self.update(path, [res[prefix_len:] for res in presults])
 
     def _add_room(self, path, results):
         label = results[0][0]
@@ -241,10 +244,13 @@ class Explore:
                 break
 
     def unexplored(self):
+        unexplored = []
         for path, ns in self.neighbors.items():
             for d, (p, rid) in enumerate(ns):
                 if not rid:
-                    yield d, path
+                    unexplored.append((d, path))
+        if unexplored:
+            yield unexplored
 
     def is_explored(self):
         return next(self.unexplored(), None) is None and all(len(p) == 1 for p in self.room_ids.values())
@@ -367,19 +373,19 @@ def mark_solve(problem, nrooms):
         ex = Explore(problem, probes)
         exs.append(ex)
 
-        res = ex.explore(Path(), mark=mark_loop)
-        ex.update(Path(), res)
+        ex.explore([Path()], mark=mark_loop)
         ex.dump()
 
         while True:
-            door, unexplored = next(ex.unexplored(), (None, None))
+            unexplored = next(ex.unexplored(), None)
             if unexplored is None:
                 break
 
-            print("explore", door, unexplored)
-            path = unexplored + Path([door])
-            res = ex.explore(path, mark=mark_loop)
-            ex.update(path, res)
+            paths = []
+            for door, path in unexplored:
+                paths.append(path + Path([door]))
+            print("explore", unexplored)
+            ex.explore(paths, mark=mark_loop)
             ex.unify_all()
             ex.dump()
 
@@ -424,7 +430,7 @@ def mark_solve(problem, nrooms):
         if t == Path():
             start = s
     print("use as start", start)
-    assert start
+    assert start is not None
 
     layout = ex.layout(orig=orig, start=starts[0])
     guess_ok = api.guess(layout)
@@ -433,60 +439,6 @@ def mark_solve(problem, nrooms):
     return guess_ok
 
 
-def path_solve(problem, nrooms, plen):
-    maxlen = 18 * nrooms
-    probe = Path([random.randrange(6) for _ in range(plen)])
-    print("probe path", probe)
-
-    ex = Explore(problem, probe)
-    api.select(ex.problem)
-
-    def extendpath(path, maxlen):
-        while len(path) < maxlen - plen - 1:
-            path = path + Path([random.randrange(6)]) + probe
-        return path
-
-    def target(door, path):
-        print("target", door, path)
-        probe0 = extendpath(probe, maxlen - len(path))
-        probe1 = extendpath(Path([door]) + probe, maxlen - len(path))
-
-        res0, res1 = ex.explore(path, [probe0, probe1])
-        ex.update_path(path, door, res0[: plen + 1], res1[: plen + 2])
-        ex.dump()
-        ex.unify_all()
-        ex.dump()
-
-        i = plen + 1
-        while i + plen < len(res0):
-            ex.update(path + probe0[:i], [res0[i : i + 1], res0[i : i + plen + 1]])
-            ex.unify_all()
-            i += plen + 1
-
-        i = plen + 2
-        while i + plen < len(res1):
-            ex.update(path + probe1[:i], [res1[i : i + 1], res1[i : i + plen + 1]])
-            ex.unify_all()
-            i += plen + 1
-
-    target(0, Path())
-    ex.dump()
-
-    while True:
-        door, unexplored = next(ex.unexplored(), (None, None))
-        print("unexplored", door, unexplored)
-        if unexplored is None:
-            break
-
-        target(door, unexplored)
-        ex.dump()
-
-    print("explored", ex.is_explored())
-    if ex.is_explored():
-        print("guess", ex.guess())
-    print("score", ex.score)
-
-
 if __name__ == "__main__":
     problem = sys.argv[1]
 
@@ -504,9 +456,9 @@ if __name__ == "__main__":
         api.clean_explore_cache()
     except ExploreError as exc:
         api.clean_explore_cache()
-        print(exc)
+        raise exc
     except Exception as exc:
         api.write_explore_cache()
-        print(exc)
+        raise exc
 
     sys.exit(0 if ok else 1)