diff --git a/doc/discretization.md b/doc/discretization.md
index 6b1f96dce5d723216b350a16fcb41480d75a19f9..cee8b0d4c3e47002a893e3fbd423186aa0dae6bc 100644
--- a/doc/discretization.md
+++ b/doc/discretization.md
@@ -194,6 +194,13 @@ We can also calculate the matrix current $`j\mapsto{}i`$ between neighboring cel
     U_{ij}
     +
     T^a U_{ij}\xi
+    \,,
+    \;
+    U_{ji}
+    \mapsto
+    U_{ji}
+    -
+    U_{ji} T^a \xi
   ]\rvert_{\xi=0}
 ```
 where $`T^a`$ is an appropriate matrix generator, and the transformation