2 files changed, 14 insertions, 0 deletions
diff --git a/lib/height.h b/lib/height.h
index a4cbbed..d2173fe 100644
--- a/lib/height.h
+++ b/lib/height.h
@@ -44,6 +44,10 @@ struct height_t {
   inline double operator*(double a) const {
     return x * a;
   }
+
+  inline T operator-(const height_t& h) const {
+    return x - h.x;
+  }
 };
 
 template <class T>
diff --git a/lib/potts.h b/lib/potts.h
index e6ea636..771c8dc 100644
--- a/lib/potts.h
+++ b/lib/potts.h
@@ -53,6 +53,16 @@ class potts_t {
 
       return result;
     }
+
+    inline vector_t<q, int> operator-(const potts_t<q> &s) const {
+      vector_t<q, int> result;
+      result.fill(0);
+
+      result[x]++;
+      result[s.x]--;
+
+      return result;
+    }
 };
 
 template <q_t q>