diff --git a/.gitignore b/.gitignore
index 37a2088..1495c09 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,6 +11,7 @@ __pycache__/*
 .cache/*
 .*.swp
 */.ipynb_checkpoints/*
+*.DS_Store
 
 # Project files
 .ropeproject
diff --git a/.travis.yml b/.travis.yml
index 7b59f70..aa63d41 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,21 +4,16 @@
 
 sudo: false
 language: python
-virtualenv:
-  system_site_packages: true
-env:
-  matrix:
-    - DISTRIB="ubuntu" PYTHON_VERSION="2.7" COVERAGE="true"
-    - DISTRIB="conda" PYTHON_VERSION="2.7" COVERAGE="false"
-    - DISTRIB="conda" PYTHON_VERSION="3.3" COVERAGE="false"
-    - DISTRIB="conda" PYTHON_VERSION="3.4" COVERAGE="false"
+python:
+    - "3.5"
 addons:
   apt:
     packages:
       - git
       - python-pip
+env:
+  - export PYTHONPATH=$TRAVIS_BUILD_DIR
 install:
-  - source tests/travis_install.sh
   - pip install -r requirements.txt
 before_script:
   - git config --global user.email "you@example.com"
diff --git a/distalg/process.py b/distalg/process.py
index 5dd6724..945f006 100644
--- a/distalg/process.py
+++ b/distalg/process.py
@@ -30,8 +30,8 @@ def _receive_msgs():
 
     def __init__(self, pid=None):
         self._id = pid or shortuuid.uuid()
-        self.in_channels = []
-        self.out_channels = []
+        self.in_channels = set()
+        self.out_channels = set()
         self.incoming_msgs = asyncio.Queue()
         self.receive_msgs = self._receive_msgs_creator()
 
diff --git a/distalg/simulation.py b/distalg/simulation.py
index 946c43f..756791d 100644
--- a/distalg/simulation.py
+++ b/distalg/simulation.py
@@ -43,8 +43,8 @@ def __init__(self, embedding_graph=None, process_type=Process, channel_type=Chan
                     channel._back = rev_channel
                     rev_channel._back = channel
 
-                process_n.out_channels.append(channel)
-                process_nbr.in_channels.append(channel)
+                process_n.out_channels.add(channel)
+                process_nbr.in_channels.add(channel)
 
     async def start_all(self):
         self.tasks += [asyncio.ensure_future(process.run()) for process in self.node_map] \
diff --git a/requirements.txt b/requirements.txt
index 4d435c8..a16de93 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,3 +13,4 @@ python-dateutil==2.6.0
 pytz==2017.2
 shortuuid==0.5.0
 six==1.10.0
+wrapt==1.10.11