diff --git a/axidence/context.py b/axidence/context.py
index 48624d3..e3c6155 100644
--- a/axidence/context.py
+++ b/axidence/context.py
@@ -15,6 +15,7 @@
     SaltedEventAmbience,
     SaltedEventSEDensity,
 )
+from axidence import EventBuilding
 
 
 def unsalted_context(**kwargs):
@@ -36,5 +37,6 @@ def salt_to_context(self):
             SaltedEventShadow,
             SaltedEventAmbience,
             SaltedEventSEDensity,
+            EventBuilding,
         )
     )
diff --git a/axidence/plugins/__init__.py b/axidence/plugins/__init__.py
index e59ac13..e8ad0f2 100644
--- a/axidence/plugins/__init__.py
+++ b/axidence/plugins/__init__.py
@@ -6,3 +6,6 @@
 
 from . import pairing
 from .pairing import *
+
+from . import cuts
+from .cuts import *
diff --git a/axidence/plugins/cuts/__init__.py b/axidence/plugins/cuts/__init__.py
new file mode 100644
index 0000000..e4c5753
--- /dev/null
+++ b/axidence/plugins/cuts/__init__.py
@@ -0,0 +1,2 @@
+from . import cut_event_building
+from .cut_event_building import *
diff --git a/axidence/plugins/cuts/cut_event_building.py b/axidence/plugins/cuts/cut_event_building.py
new file mode 100644
index 0000000..4edbd5a
--- /dev/null
+++ b/axidence/plugins/cuts/cut_event_building.py
@@ -0,0 +1,14 @@
+from strax import CutPlugin
+
+
+class EventBuilding(CutPlugin):
+    __version__ = "0.0.0"
+    depends_on = "event_basics"
+    provides = "cut_event_building"
+    cut_name = "cut_event_building"
+    cut_description = "Whether the salting S1 or S2 can be the main S1 or S2"
+
+    def cut_by(self, events):
+        mask = events["s1_salt_number"] >= 0
+        mask &= events["s2_salt_number"] >= 0
+        return mask
diff --git a/tests/test_deps_tree.py b/tests/test_deps_tree.py
index 7261b76..d28f78c 100644
--- a/tests/test_deps_tree.py
+++ b/tests/test_deps_tree.py
@@ -5,6 +5,6 @@ def test_deps_tree():
     """This test can tell us whether the dependency tree is correct or not."""
     st = axidence.unsalted_context()
     st.salt_to_context()
-    st.dependency_tree("event_shadow", to_dir="./graphs_nT")
-    st.dependency_tree("event_ambience", to_dir="./graphs_nT")
-    st.dependency_tree("event_se_density", to_dir="./graphs_nT")
+    graph_dir = "./graphs_nT"
+    for p in ["event_shadow", "event_ambience", "event_se_density", "cut_event_building"]:
+        st.dependency_tree(p, to_dir=graph_dir)