diff --git a/coix/loss.py b/coix/loss.py
index cbef1c5..1a10fec 100644
--- a/coix/loss.py
+++ b/coix/loss.py
@@ -29,7 +29,13 @@
 ]
 
 
-def apg_loss(q_trace, p_trace, incoming_log_weight, incremental_log_weight, aggregate=False):
+def apg_loss(
+    q_trace,
+    p_trace,
+    incoming_log_weight,
+    incremental_log_weight,
+    aggregate=False,
+):
   """RWS objective that exploits conditional dependency."""
   del incoming_log_weight, incremental_log_weight
   p_log_probs = {