diff --git a/demo/demo.yaml b/demo/demo.yaml
index 1f87bc8..1d04519 100644
--- a/demo/demo.yaml
+++ b/demo/demo.yaml
@@ -1,6 +1,6 @@
 title: Example
 database: students.db
-path: ./demo
+# path: ./demo
 
 # values applie to each topic, if undefined there
 # default values are: file=question.yaml, shuffle=True, choose: all
@@ -17,7 +17,6 @@ forgetting_factor: 0.99
 #         - B
 #         - C
 topics:
-
   # topic without dependencies
   math:
     name: Matemática
diff --git a/demo/solar_system/questions.yaml b/demo/solar_system/questions.yaml
index 2164fa2..ac57804 100644
--- a/demo/solar_system/questions.yaml
+++ b/demo/solar_system/questions.yaml
@@ -38,13 +38,13 @@
 #     correct: !regex '[Ss]aturno'
 
 # ---------------------------------------------------------------------------
-- ref: first_3_planets
-  type: textarea
-  title: Sistema solar
-  text: Escreva o nome dos três planetas mais próximos do Sol. (Exemplo `A, B e C`)
-  correct: correct-first_3_planets.py
-  # correct: correct-timeout.py
-  # opcional
-  answer: Vulcano, Krypton, Plutão
-  lines: 3
-  timeout: 50
+# - ref: first_3_planets
+#   type: textarea
+#   title: Sistema solar
+#   text: Escreva o nome dos três planetas mais próximos do Sol. (Exemplo `A, B e C`)
+#   correct: correct-first_3_planets.py
+#   # correct: correct-timeout.py
+#   # opcional
+#   answer: Vulcano, Krypton, Plutão
+#   lines: 3
+#   timeout: 50
diff --git a/knowledge.py b/knowledge.py
index e2cb796..8dbf560 100644
--- a/knowledge.py
+++ b/knowledge.py
@@ -70,7 +70,7 @@ class StudentKnowledge(object):
     #    questions: list of generated questions to do in the topic
     #    current_question: the current question to be presented
     # ------------------------------------------------------------------------
-    def init_topic(self, topic):
+    async def init_topic(self, topic):
         logger.debug(f'StudentKnowledge.init_topic({topic})')
 
         # do not allow locked topics
@@ -88,7 +88,7 @@ class StudentKnowledge(object):
         self.wrong_answers = 0
 
         # select a random set of questions for this topic
-        size = min(self.MAX_QUESTIONS, len(questionlist)) # number of questions
+        size = len(questionlist) # number of questions FIXME get from topic config
         questionlist = random.sample(questionlist, k=size)
         logger.debug(f'Questions: {", ".join(questionlist)}')
 
diff --git a/learnapp.py b/learnapp.py
index 8e17b6e..8979ed4 100644
--- a/learnapp.py
+++ b/learnapp.py
@@ -22,8 +22,8 @@ from tools import load_yaml
 logger = logging.getLogger(__name__)
 
 # ============================================================================
-class LearnAppException(Exception):
-    pass
+# class LearnAppException(Exception):
+#     pass
 
 
 # ============================================================================
@@ -61,11 +61,11 @@ class LearnApp(object):
             session.close()
 
     # ------------------------------------------------------------------------
-    def __init__(self, config_files):
+    def __init__(self, config_files, prefix):
         self.db_setup()       # setup database and check students
         self.online = dict()  # online students
 
-        self.deps = nx.DiGraph()
+        self.deps = nx.DiGraph(prefix=prefix)
         for c in config_files:
             self.populate_graph(c)
 
@@ -192,9 +192,9 @@ class LearnApp(object):
     # Start new topic
     # ------------------------------------------------------------------------
     async def start_topic(self, uid, topic):
-        loop = asyncio.get_running_loop()
+        student = self.online[uid]['state']
         try:
-            await loop.run_in_executor(None, self.online[uid]['state'].init_topic, topic)
+            await student.init_topic(topic)
         except KeyError as e:
             logger.warning(f'User "{uid}" tried to open nonexistent topic: "{topic}"')
             raise e
@@ -277,9 +277,9 @@ class LearnApp(object):
     # ------------------------------------------------------------------------
     def get_current_public_dir(self, uid):
         topic = self.online[uid]['state'].get_current_topic()
-        p = self.deps.graph['path']
-        return path.join(p, topic, 'public')
+        p = self.deps.graph['prefix']  # FIXME not defined!!!
 
+        return path.join(p, topic, 'public')
 
 
     # ============================================================================
@@ -304,21 +304,12 @@ class LearnApp(object):
         g = self.deps                   # the graph
         config = load_yaml(conffile)    # course configuration
 
-        # set attributes of the graph
-        prefix = path.expanduser(config.get('path', '.'))
-        # title = config.get('title', '')
-        # database = config.get('database', 'students.db')
-
         # default attributes that apply to the topics
         default_file = config.get('file', 'questions.yaml')
         default_shuffle = config.get('shuffle', True)
         default_choose = config.get('choose', 9999)
         default_forgetting_factor = config.get('forgetting_factor', 1.0)
 
-        # create graph
-        # g = nx.DiGraph(path=prefix, title=title, database=database, config=config)
-
-
         # iterate over topics and populate graph
         topics = config.get('topics', {})
         tcount = qcount = 0   # topic and question counters
@@ -331,12 +322,12 @@ class LearnApp(object):
             g.add_node(tref)
             t = g.node[tref]  # current topic node
 
-            topicpath = path.join(prefix, tref)
+            topicpath = path.join(g.graph['prefix'], tref)
 
             t['type'] = attr.get('type', 'topic')
             t['name'] = attr.get('name', tref)
-            t['path'] = topicpath
-            t['file'] = attr.get('file', default_file)
+            t['path'] = topicpath                       # prefix/topic
+            t['file'] = attr.get('file', default_file)  # questions.yaml
             t['shuffle'] = attr.get('shuffle', default_shuffle)
             t['forgetting_factor'] = attr.get('forgetting_factor', default_forgetting_factor)
             g.add_edges_from((d,tref) for d in attr.get('deps', []))
diff --git a/questions.py b/questions.py
index 038a8ff..2d37fe4 100644
--- a/questions.py
+++ b/questions.py
@@ -154,7 +154,7 @@ class QuestionCheckbox(Question):
         # set defaults if missing
         self.set_defaults({
             'text': '',
-            'correct': [0.0] * n,     # useful for questionaries
+            'correct': [1.0] * n,     # Using 0.0 breaks the (right, wrong) options
             'shuffle': True,
             'discount': True,
             'choose': n,              # number of options
diff --git a/serve.py b/serve.py
index dcd93ed..273beab 100755
--- a/serve.py
+++ b/serve.py
@@ -304,9 +304,11 @@ def main():
     # --- Commandline argument parsing
     argparser = argparse.ArgumentParser(description='Server for online learning. Enrolled students and topics have to be previously configured. Please read the documentation included with this software before running the server.')
     argparser.add_argument('conffile', type=str, nargs='+',
-        help='Topics configuration file in YAML format.') # FIXME only one
+        help='Topics configuration file in YAML format.')
+    argparser.add_argument('--prefix', type=str, default='demo',
+        help='Path prefix under which the topic directories can be found, e.g. ~/topics')
     argparser.add_argument('--port', type=int, default=8443,
-        help='Port to be used by the HTTPS server')
+        help='Port to be used by the HTTPS server, e.g. 8443')
     argparser.add_argument('--debug', action='store_true',
         help='Enable debug messages')
     arg = argparser.parse_args()
@@ -327,7 +329,7 @@ def main():
     # --- start application
     logging.info('Starting App')
     try:
-        learnapp = LearnApp(arg.conffile)
+        learnapp = LearnApp(arg.conffile, prefix=arg.prefix)
     except Exception as e:
         logging.critical('Failed to start backend application')
         raise e
--
libgit2 0.21.2