diff --git a/src/kyupy/sim.py b/src/kyupy/sim.py
index 32b7459..765a394 100644
--- a/src/kyupy/sim.py
+++ b/src/kyupy/sim.py
@@ -233,6 +233,7 @@ class SimOps:
         self.levels = [np.asarray(lv, dtype=np.int32) for lv in levels[::-1]]
         level_sums = np.cumsum([0]+[len(lv) for lv in self.levels], dtype=np.int32)
         self.level_starts, self.level_stops = level_sums[:-1], level_sums[1:]
+        # op format: [kind, out0, in0, in1, in2, in3, wsa_acc_pos, wsa_rise, wsa_fall]
         self.ops = np.vstack(self.levels)
 
         # create a map from fanout lines to stem lines for fork stripping
diff --git a/tests/test_circuit.py b/tests/test_circuit.py
index d4edcd3..834c53f 100644
--- a/tests/test_circuit.py
+++ b/tests/test_circuit.py
@@ -131,7 +131,14 @@ def test_pickle(mydir):
     cs = pickle.dumps(c)
     assert cs is not None
     c2 = pickle.loads(cs)
-    assert c == c2
+    assert len(c.nodes) == len(c2.nodes)
+
+def test_equivalency():
+    c1 = bench.parse('input(a) output(z) z=not(a)')
+    c2 = bench.parse('input(a) output(z) z=not(a)')
+    assert c1 != c2
+    assert c1.lines[0] != c2.lines[0]
+    assert c1.nodes[0] != c2.nodes[0]
 
 
 def test_substitute():